Flash vaporization surgical systems

ABSTRACT

A laser can produce pulses of light energy to eject a volume of the tissue, and the energy can be delivered to a treatment site through a waveguide, such as a fiber optic waveguide. The incident laser energy can be absorbed within a volume of the target tissue with a tissue penetration depth and pulse direction such that the propagation of the energy from the tissue volume is inhibited and such that the target tissue within the volume reaches the spinodal threshold of decomposition and ejects the volume, for example without substantial damage to tissue adjacent the ejected volume.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/092,847 filed on 22 Apr. 2011 (now U.S. Pat. No. 8,881,735), whichapplication is a continuation-in-part of PCT/US2009/065002, filed on 18Nov. 2009, designating the United States, which internationalapplication claims the benefit of U.S. Provisional Application No.61/115,793 filed on 18 Nov. 2008, and which application claims thebenefit of U.S. Provisional Application No. 61/327,060 filed on 22 Apr.2010, and claims the benefit of U.S. Provisional Application No.61/370,727 filed on 4 Aug. 2010.

BACKGROUND OF THE INVENTION

Well controlled tissue removal can be an important aspect of surgery. Inat least some instances the ability of a surgeon to perform an incisionwithout substantially affecting the surrounding tissue, for example thetissue adjacent to the resection site, can be clinically helpful. Formany surgical procedures, it would be beneficial to avoid, or at leastdecrease, injury to the adjacent tissue. Furthermore, it can bebeneficial for a surgeon to use a resection tool that is capable ofreaching a remote surgical site, such as a treatment site accessedendoscopically.

A variety of tools have been developed to remove vascular soft tissue,cartilage and bone during surgical procedures, and many of these priortools can be less than ideal for tissue cutting, for example of aninternal surgical site. Mechanical instruments such as scalpels, bitersand curettes along with powered mechanical instruments such asmicrodebriders and drills have been employed. Mechanical devices may cuttissue with varying degrees of localization and in at least someinstances can induce mechanical trauma to the tissue. Although energydelivery based devices such as radio frequency, ultrasonic, and lasershave been used for tissue removal, these devices can have disadvantagesin at least some instances. For example, when tissue is inadvertentlyremoved or damaged by mechanical or thermal injury the clinical outcomeand patient recovery can be adversely affected in at least someinstances.

Radio frequency (RF) devices have been for tissue removal, and the priorRF devices can result in less than ideal tissue cutting. Although RFdevices can be used to cut tissue by thermal and/or plasma mediatedmechanisms, RF devices can cause at least some level of thermal injuryin the adjacent tissue in at least some instances. In at least someinstances, thermal injury may occur to the tissue adjacent to the cut.Also, RF devices can introduce accessibility and maneuverabilitychallenges for surgeons, such as endoscopic surgeons in at least someinstances.

Although prior laser based energy devices have been used for tissueremoval, these laser systems can cut tissue more slowly than would beideal and can injure the tissue adjacent to the cut. For example,thermal injury can occur in the tissue adjacent the cut with at leastsome commercially available medical laser systems. In at least someinstances, the prior laser systems can be characterized by a HeatAffected Zone (HAZ) in front of an ablation zone. The laser energy canbe introduced to the target tissue over time sufficient to raise thetemperature and ablate tissue. In at least some instances the ablationprocess can be accompanied by charring of collateral tissue along with asignificant HAZ which can be detrimental to the healing process.Although some pulsed laser systems such as UV, photospallation, andultrashort pulse laser systems may ablate tissue with somewhat decreasedthermal damage as compared to continuous wave systems, in many instancespulsed laser systems may not cut tissue quickly and an ablation plumecan interfere with a subsequent laser beam pulses such that increasingthe rate of laser beam pulses may not adequately increase the rate oftissue removal in at least some instances.

Although UV based laser systems such as excimer laser systems have beenused for tissue ablation, the UV based systems can have a shallow perpulse penetration depths and may result in tissue mutagenic effects inat least some instances. The pulse rate and shallow depth per pulseablation depths can make UV based laser systems less than ideal fortissue removal in at least some instances. Also, the light from UV basedlaser systems can have less than ideal delivery through optical fibers,such that access to internal surgical sites can be limited in at leastsome instances. The generally slow overall depth penetration ablationrates, limited fiber delivery, and complexity can make UV laser systemsless than ideally suited for tissue resection requiring larger cuts, inat least some instances. For example, with endoscopic surgicalprocedures light energy is delivered through an optical fiber and tissueis cut to a substantial depth along a substantial length, such that UVexcimer laser systems are not well suited for endoscopic tissue cuttingin at least some instances.

Although prior pulsed infrared lasers have been used to ablate tissuewith photospallation, photospallation can be less than ideal for cuttingtissue in at least some instances, such as endoscopically.Photospallation can have shallow per pulse ablation depths, such as afew microns, and photospallation based systems can have pulse ratelimitations, such that the overall tissue cutting rate may be too slowfor practical use. Also, photospallation systems can use opticalwavelengths that are strongly absorbed by optical fibers, such thatdelivery to internal surgical sites on a patient may not be possible.Photospallation systems can be less than ideal for tissue resection dueto very slow cutting rates and no practical means to deliver the laserenergy for most endoscopic procedures.

Although prior ultrashort pulse laser technology such as femtosecond andpicosecond laser systems can ablate tissue with an ionization process,the total energy per individual pulse can be very small and result insmall amounts of tissue ablated. Also, the high peak powers can beunsuitable for fiber optic waveguides in at least some instances.Therefore, ultrashort pulse lasers can be less than ideal for tissueresection with larger cuts, such as in endoscopic surgical procedures.

Therefore, it would be helpful to provide improved methods and apparatusfor cutting tissue that overcome at least some of the above limitationof the prior systems. Ideally, such methods and apparatus would providesurgeons a fast and effective cutting tool with flexibility to performmany sizes of tissue resections with precise localization, includingcutting tissue without substantial thermal or mechanical damage on thetissue adjacent to the cut, for example. It would also be helpful ifsuch methods and apparatus could accurately cut tissue withoutsubstantial tissue damage at an internal patient location with aflexible waveguide, for example with a flexible silica fiber forendoscopic procedures. Additionally methods and apparatus for tissuecutting that are applicable to a broad variety of tissue types may beimportant to surgeons and/or necessary to effectively perform certainprocedures.

BRIEF SUMMARY

Methods and apparatuses are described to quickly and efficiently removeand resect tissue without substantial thermal or mechanical damage tothe adjacent tissue. Delivery tools and control technologies aredescribed that enable surgical techniques utilizing the tissue removaltechnologies. These technologies address the problems discussed above,and enable new classes of laser surgery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a-1b show the absorption coefficient and optical penetration depth(hereinafter “OPD”) in water as a function of wavelength.

FIG. 2a-2c show a representative interaction volume depth to widthratio, in accordance with embodiments.

FIG. 3 shows a laser system utilizing Flash Vaporization for tissueremoval during laparoscopic surgery, in accordance with embodiments.

FIG. 4 shows a laser system for implementing a Flash Vaporization basedsurgical device, in accordance with embodiments.

FIG. 5 shows a laser resonator for implementing Flash Vaporization, inaccordance with embodiments.

FIG. 6 shows a bar chart comparing cutting rates for various forms ofresection, in accordance with embodiments.

FIGS. 7A and 7B are images showing histology obtained from tissueresection performed with a laser system, in accordance with embodimentsas described herein.

FIG. 8 shows tissue removal for single fiber Flash Vaporization systemversus a 4 fiber Flash Vaporization system.

FIG. 9 shows a multi-fiber delivery system where the individual fiberoutputs are overlapped at the treatment site.

FIG. 10 shows an alternative multi-fiber delivery system where theindividual fiber outputs are overlapped at the treatment site.

FIGS. 11a and 11b show a multi-fiber delivery device tip with theoutputs arranged linearly and adjacent to one another and an exemplarydirection of motion.

FIG. 12 shows an exemplary multi-fiber device configured to mimic ascalpel.

FIG. 13 shows an alternative direction of motion for a linear fiber tiparrangement.

FIGS. 14a-14c show exemplary multi-fiber device tip configurations forrapid tissue ablation.

FIGS. 15a-15b shows directions of motion and exemplary multi-fiberdevice configurations.

FIG. 16 shows an exemplary multi-fiber device tip configuration forgenerally spherical tumors.

FIG. 17 shows an exemplary multi-fiber device tip configuration forgenerally cylindrical tumors.

FIG. 18 shows an exemplary multi-fiber device tip configuration for pacemaker lead removal.

FIG. 19 shows an exemplary multi-fiber device tip configuration forusing a painting motion to rapidly ablate tissue.

FIG. 20 shows an exemplary means to couple laser energy into multipledelivery fibers.

FIG. 21 shows a simple multi-fiber device tip with the coagulation fiberoffset further from the treatment site than the Flash Vaporizationfiber.

FIG. 22 shows an exemplary multi-fiber device tip configuration withonly the center fiber enabled.

FIGS. 23a-23d shows an exemplary multi-fiber device tip configurationwhere the number of enabled fibers varies to suite the clinical need.

FIGS. 24-27 are plots illustrating aspects of the parameter space whichmust be taken into consideration in systems employing flash vaporizationis described herein.

FIG. 28A shows a laser surgery system with an endoscopic probe insertedinto a nasal cavity of a patient, according to embodiments of thepresent invention.

FIG. 28B shows the laser system of FIG. 28A for implementing a versatileand effective surgical tool with enhanced clinical capabilities,according to embodiments of the present invention.

FIG. 29A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a pump pulse mode for thermal depositionto tissue.

FIG. 29B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a pump pulse mode for cutting tissue.

FIG. 30A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a pump pulse mode of linearly increasingpulse duration, period and amplitude.

FIG. 30B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a periodic pump pulse mode of decreasingpulse duration and period.

FIG. 30C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a pump pulse mode to maintain arelatively constant cutting rate with more coagulation at the beginningof the exposure.

FIG. 30D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a pump pulse mode to create a relativelyuniform coagulation zone around the contour of the cut region.

FIG. 31A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode of less cuttingefficient and more thermal deposition.

FIG. 31B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode of more cuttingefficient and less thermal deposition.

FIG. 32A shows an exemplary output waveform of the laser as in FIG. 28 Bwhen the system is operated in a q-switched pulse mode of linearlyincreasing pulse duration, period and amplitude.

FIG. 32B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a periodic q-switched pulse mode ofdecreasing pulse duration and period.

FIG. 32C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to ablate bone.

FIG. 32D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to cut tissue anddeposit more heat to control bleeding.

FIG. 32E shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to remove a nervesheath.

FIG. 32F shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to coagulate aruptured vessel.

FIG. 33 shows the absorption characteristics of blood and water intissue over a broad spectral range, for incorporation in accordance withembodiments of the present invention.

FIG. 34 shows a laser system with two complimentary output wavelengthsfor implementing a versatile and effective surgical tool with furtherenhanced clinical capabilities, in accordance with embodiments of thepresent invention.

FIG. 35 shows a cross-section of an inferior turbinate, showing anexemplary tissue effect of the laser as in FIG. 28B or FIG. 34 lasersystem.

FIG. 36 shows a plot of ablation rate as a function of radiant exposure.

FIG. 37A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed pump pulse parameters and a shorter q-switch period.

FIG. 37B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed pump pulse parameters and a longer q-switch period.

FIG. 37C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed q-switch pulse parameters and a longer pump pulse duration.

FIG. 37D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed q-switch pulse parameters and a shorter pump pulse duration.

FIG. 37E shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith a longer pump pulse duration and a longer q-switch pulse period.

FIG. 37F shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith a shorter pump pulse duration and a shorter q-switch pulse period.

FIG. 38A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith increasing pump pulse duration and decreasing q-switch pulse periodwithin each pump pulse.

FIG. 38B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modeincreasing pump pulse duration and decreasing q-switch pulse periodacross a multiple pump pulse exposure.

FIG. 38C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an increasing pump pulse duration and a fixed longer q-switch pulseperiod.

FIG. 38D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an increasing pump pulse duration and a q-switch pulse period thatis fixed during each pump pulse and decreasing with each subsequent pumppulse.

FIG. 39A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an abrupt transition from less thermal deposition to more thermaldeposition.

FIG. 39B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an abrupt transition from more thermal deposition to less thermaldeposition.

FIG. 39C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an abrupt transition from more thermal deposition to less thermaldeposition, repeated during each pump pulse.

FIG. 39D shows the pump source and q-switch modulation individually andthe resulting laser output waveform of the laser as in FIG. 28B when thesystem is operated in a combined q-switched and pump pulse mode with anabrupt transition from more thermal deposition to less thermaldeposition, repeated during each pump pulse.

FIG. 39E shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith the q-switch mode including a continuous wave portion.

FIG. 39F shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith the q-switch mode including a variable amplitude continuous waveportion.

FIG. 40 shows an exemplary simple slide bar user interface with dynamicpulsing, in accordance with embodiments of the present invention.

FIG. 41 shows an exemplary flow diagram for interpreting the usersettings and establishing the laser output pulsing scheme, in accordancewith embodiments of the present invention.

FIG. 42 shows an exemplary touch screen user interface for customizingdynamic pulse parameters without transitions during exposures, inaccordance with embodiments of the present invention.

FIG. 43 shows a flow diagram of an exemplary control system for dynamicpulsing with an user interface as depicted in FIG. 42, including anexemplary flow diagram for interpreting the user settings andestablishing the dynamic pulsing scheme without transitions duringexposures, in accordance with embodiments of the present invention.

FIG. 44 shows an exemplary touch screen user interface for customizingdynamic pulse parameters with transitions during the exposure, inaccordance with embodiments of the present invention.

FIG. 45 shows a flow diagram of an exemplary control system fortransitional dynamic pulses and an user interface as depicted in FIG.44, including an exemplary flow diagram for interpreting the usersettings and establishing the pulsing scheme with dynamic pulsetransitions during an exposure, in accordance with embodiments of thepresent invention.

FIG. 46 shows a laser system using an end-pumping scheme to pump thegain medium, in accordance with embodiments of the present invention.

FIG. 47 shows representative tissue effects and their correspondingdynamic pulse schemes, in accordance with embodiments of the presentinvention.

FIG. 48 Pulsed treatment time sequence of dynamic pulse scheme in FIG.32D, showing the timing sequence of tissue effects for representativedynamic pulse schemes, in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention as described herein provide fastand efficient laser based cutting. The laser based cutting modality asdescribed herein is applicable to a variety of tissue types andsurgeries, such that there is no substantial thermal or mechanicaldamage or effect on the tissue adjacent to the cut.

One species of a more generic class of methods for removing tissueincludes producing laser pulses having a wavelength between 1880 and2080 nm or between 2340 and 2500 nm, having between 1 and 10 milliJoulesper pulse, and having a pulse length less than 100 nsec; and deliveringthe pulses to a spot on the tissue; whereby an interaction volumedefined by the area of the spot and the penetration depth (1/e) for thepulse in water has a ratio of depth to width from 2:1 to 1:6. The methodcan include delivering the laser pulses to the target tissue using afiber optic having a core diameter in the range of 10 to 300, preferably50 to 200 um. The waveguide used to deliver the pulses can comprise asilica optical fiber. The method can include utilizing pulse repetitionrates from single shot to 2000 Hz. Utilizing this method, the appliedenergy heats the interaction volume of the tissue above a spinodaldecomposition threshold for water within the pulse duration, translatinglaser energy into kinetic energy, via spinodal decomposition, leading tohighly efficient ejection of tissue within the interaction volume.Furthermore, the laser pulses have a pulse duration sufficiently shortto prevent stress waves and heat from propagating beyond the interactionvolume relative to a shortest dimension of the interaction volume. Thevolumetric power density delivered to each spot can be greater than 10¹⁰W/cm³ for each pulse. As a result, most, if not essentially all, of theenergy of the laser pulse is dissipated in the tissue that is removed bythe pulse. It is found that using this method as applied to tissueincluding a sufficient water to produce pressure for ejection of thetissue infrastructure, and unlike any known prior art, significantvolumes tissue can be removed with no apparent thermal injury to thetissue adjacent the cavity left by the ablation.

Another more general method includes producing laser pulses having awavelength between 1400 and 1520 nm or between 1860 and 2500 nm, havingbetween 0.5 and 40 milliJoules per pulse, and having a pulse length lessthan 200 nsec, preferably less than 100 ns; and delivering the pulses toa spot on the tissue using a waveguide such as a silica optical fiberhaving a core diameter in a range of 50 um to 200 um. Using thistechnology, an interaction volume defined by the area of the spot andthe penetration depth (1/e) for the pulse in water has a ratio of depthto width from 2:1 to 1:6. The energy per pulse and wavelengths can beadjusted for interaction with other chromophores, and to producepressures needed for various tissue types within this range.

According to a more general embodiment, a method for tissue removal,comprises producing laser pulses having a wavelength between 1400 and1520 nm or between 1860 and 2500 nm, and having a pulse duration; anddelivering the laser pulses to a spot on the tissue, the laser pulseshaving an energy per pulse (E_(p)) to heat an interaction volume of thetissue above a spinodal decomposition threshold for water within thepulse duration, and cause sufficient pressure for ejection of the targettissue, and having a pulse duration sufficiently short to prevent stresswaves or heat from propagating beyond the interaction volume relative toa shortest dimension of the interaction volume. The method can becharacterized more generally by the steps of producing laser pulseshaving a wavelength (λ) and pulse duration (t_(p)); and delivering asequence of the laser pulses to respective spots having impact areas (A,e.g. πr²) on the tissue and having a penetration depth in the tissue,the pulses having a nominal interaction volume in the tissue that is afunction of the impact areas and the penetration depth; whereby aninteraction volume defined by the area of the spot and the penetrationdepth (1/e) for the pulse in water, the interaction volume having aratio of depth to width from 2:1 to 1:6.

The pulse duration in a more general genus of the method is less than200 nsec and the pulse has a peak power density E/(t_(p)A) below thethreshold for inducing significant plasma formation. This method cancomprise of delivering the sequence laser pulse using a silica opticalfiber, with energy and pulse duration combinations that are below thedamage threshold for the silica optical fiber. The method can be furthercharacterized by an impact area having a dimension equal to a smallestdistance across the impact area, and the pulse duration is within 3times of a stress confinement duration of the time for propagation of anacoustic wave a lesser of one-half said dimension (e.g. r) and thepenetration depth. The method can include laser pulses interacting withthe interaction volume with a volumetric power density greater than 10¹⁰W/cm³.

According to a species of the more general method described herein, alaser including a Tm:YAP gain medium is arranged to produce an outputwavelength near 1940 nm. The laser is used to deliver a sequence ofpulses a tissue site, with an energy per pulse in the range of 1 to 10mJ per pulse in pulse widths less than 100 nsec, with a beam deliverytool, such as a fiber optic or other waveguide. The method includesdelivering the pulses to the treatment site with a spot size of 50 to200 microns. A wavelength near 1940 nm has an optical penetration depthin water of about 80 microns. Because water is a primary component ofmost tissues, the penetration depth in tissue can be approximately thesame. Using a spot size and an 80 micron penetration depth, one candetermine the dimensions of an interaction volume within the tissue atthe treatment site for a laser pulse. Using a pulse width less than 100nsec, such as between 10 nsec and 50 nsec for a representativeprocedure, results in a condition of thermal and mechanical confinementof the energy dissipation from the laser pulse, within that interactionvolume. Using an energy per pulse on the order of 0.5 to 40 mJ issufficient in this example to generate greater than 5×10¹⁰ W/cm³ withinthe interaction volume and raise the temperature of the water in theinteraction volume above the spinodal limit, can cause confined spinodaldecomposition of the water. The spinodal decomposition results in aninstantaneous phase change that creates substantial pressure in a rangeof about 200 bars to 10 kBars within the interaction volume at thetreatment site. Energy in a pulse sufficient to induce the spinodaldecomposition, is translated via this confined pressure into kineticenergy that can eject the tissue without visible thermal damage totissue adjacent to the ejected volume, such as would otherwise be causedby thermal or acoustic waves induced by the ejection or the laser pulse.This effect is termed herein Flash Vaporization. The laser systemaccording to this species can be operated with repetition rates fromsingle shot to 2000 Hz, and because of the substantial volume of tissueejected with each pulse, cutting rates can be achieved using FlashVaporization that have not been possible using known prior arttechniques.

Other species of the method within this more generic class can utilizelasers operating in wavelengths that have similar optical penetrationdepths in tissue having water as a primary component, includingwavelengths between 1400 and 1520 nm or between 1860 and 2500 nm.Wavelengths in this range are also characterized by the fact that theyare readily deliverable using silica waveguides on the order of 10 to300 microns, preferably 50 to 200 microns in core diameter within theenergy per pulse in the range of 0.5 to 40 mJ per pulse and pulse widthsbetween about 10 nsec and 200 nsec. In some embodiments, the energy perpulse can range from about 100 uJ to about 100 mJ. Furthermore manyembodiments embodiment for flash tissue vaporization using water as thechromophore utilizes pulse energies from 500 uJ to 30 mJ. Specificembodiments for Flash Vaporization can use water as the chromophore anda wavelength near 1.94 μm, pulse widths between 10 ns and 100 ns andpulse energies from 1 mJ to 10 mJ. Because of the availability andbiocompatibility of silica waveguides, these species of laser systemscan be readily utilized in a wide variety of endoscopic laser surgeries.

As spot size increases, the energy per pulse needed to achieve ejectionby spinodal decomposition increases significantly. This limits the sizeof a laser spot that can be practically used in laser surgeryapplications. Other species described herein are configured to removelarger volumes of tissue per unit time. Such species utilize laserscapable of producing outputs that are a multiple of the energy per pulseto be applied by each pulse. In such species, a delivery tool includingmultiple waveguides can be coupled to the laser system for delivery ofmultiple spots, preferably adjacent, of laser energy to the treatmentsite in parallel or in rapid sequence. As there is essentially noresidual energy in the tissue after ejection, the multiple spots aretreated essentially independently. Multiple spots can be used to achievevery high tissue removal rates with no apparent residual injury to thetissue adjacent the cavity left by the ejected tissue.

It is recognized that different tissue types may require differentparameters to achieve flash vaporization and eject substantially all ofthe material within the interaction volume. Thus a more generic class oflaser systems as described herein can be characterized by including alaser to generate a pulsed beam of light energy, each pulse of the beamto irradiate a volume of tissue and having a duration and an amount ofenergy to inhibit mechanical energy, or stress, and thermal energypropagation from the volume such that the volume of the tissue isejected with spinodal decomposition; and a controller coupled to thelaser to generate the pulsed light beam in response to commands from thecontroller. The system can be combined with an endoscopic delivery tool,including one or more optical fibers. Laser surgery based on flashvaporization can be performed within a complex parameter space describedin more detail below. The discovery of commercially feasible operatingconditions for lasers and delivery tools as described herein enables forthe first time, a new variety of “cold ablation” surgical techniques.

Flash Vaporization as described herein can use pulsed laser energy toefficiently ablate tissue such that the incident laser energy absorbedby tissue is substantially converted from thermal to kinetic energy thatis ejected from the treatment site to remove tissue. As a majority ofthe energy deposited with each pulse can be translated into kineticenergy confined within the tissue volume, any thermal or mechanicalenergy imparted into the adjacent tissue is substantially decreased, andin some instances essentially eliminated.

The lower overall power requirements provide an advantage in the sizeand power consumption of the laser itself. A non limiting example oflaser energy characteristics as delivered to tissue to achieve FlashVaporization, ablation with negligible thermal or mechanical injury tothe adjacent tissue, include energy per pulse, pulse width, targetvolume, target shape, wavelength and repetition rate.

A means to deliver the laser energy to the treatment site can includesilica waveguides, doped silica waveguides, non silica based solid corewaveguides, hollow core waveguides and free space beam delivery,including articulating arms. Laser based cutting tools can be used withmany surgical approaches, including endoscopic surgery. For manysurgical procedures, including endoscopic surgery, it is desirable todeliver the laser energy through a low cost, biocompatible, small andflexible waveguide, such as a silica optical fiber waveguide, having anenergy transmission efficiency of at least about 80%.

Flash Vaporization can be used for surgical applications. FlashVaporization provides surgeon the ability to cut tissue, even inendoscopic applications, for example without substantial thermal ormechanical residual effects to the adjacent tissue. The cutting tip canbe very small, sub-millimeter, and flexible. The laser based flashvaporization cutting tool can be easily positioned and maneuvered at asurgical treatment site. Additionally flash vaporization may not applymechanical pressure, such as a scalpel would, on the tissue to create acut. Flash vaporization is well suited for surgical applications wherethermal or mechanical injury to the adjacent tissue is undesirable. Forexample removal of diseased tissue that has grown around a nerve bundleis an advantageous application of flash vaporization. Preciselycontrolling the location of the cut along with negligible thermal ormechanical injury to the nerve bundle itself is useful in thisapplication. Pulse by pulse operation with microscopic imaging allow forvery precise cutting. Flash vaporization can provide surgeons withcapability to safely remove tissue with high precision and withoutimpacting the surround tissue. Surgeons can achieve better outcomes,efficiently with less risk to the patient.

Flash vaporization may be combined simultaneously or serially with otherthermal based treatment modalities so as to provide heat inducedhemostatic capability surrounding the cut, for certain surgicalapplications when hemostasis is desirable.

The flash vaporization ablation mechanism can ablate tissue withnegligible thermal affects adjacent to the ejected tissue. Flashvaporization can achieve cutting rates with negligible residual damageto the adjacent tissue. Flash vaporization can cut tissue with fastcutting rates. Flash vaporization can be achieved with wavelengths oflight energy delivered through standard silica fibers, for example.Clinically a flash vaporization based laser system offers very fastcutting rates when delivered through a commercially available opticalfiber waveguide. Flash vaporization may comprise a high efficiency rateso as to cut tissue with a low average power laser generator whichallows the system to be sized to fit in a physician's office withportability and reliability. Utilizing a flash vaporization basedresection system allows the surgeons to readily access many surgicalsites of the patient, for example endoscopically, and can cut many typesof tissue while preserving adjacent tissue to produce better surgicaloutcomes with less risk and a faster recovery period for their patients.

Flash vaporization can include the incident laser energy being absorbedby a chromophore in the target tissue. Non limiting examples of typicalchromophores for laser energy interaction with tissue may include water,blood, collagen and melanin. It can be desirable to select a chromophorethat is present in a wide range of tissue types with sufficient quantityto be effectively targeted. Water is the target chromophore for manyembodiments.

The rapid cutting rates achieved with flash tissue vaporization are canbe achieved with a deep optical penetration depth OPD. Many embodimentsuse OPDs of at least 70 um to achieve significantly faster cuttingrates.

Spinodal decomposition may comprise a phase change of water from liquidto gas that may occur substantially uniformly within a target volume. Byelevating the water temperature within the volume to approximately 300°C. or greater, for example, within a time frame sufficient to initiatespinodal decomposition. The water in the volume can undergo a spatiallyand temporally uniform phase change, resulting in pressure inducedkinetic energy such that the tissue can be ejected with inhibited damageto tissue adjacent to the target volume after each pulse. The energyreleased as a result of the uniform phase change can create stressesthat are used to eject the volume.

Flash vaporization can occur with a laser beam pulse by elevating atarget volume to a temperature at or in excess of the spinodal thresholdfor water, in which the target volume can be determined by the incidentenergy laser beam spot size and the OPD. Also, the spinodaldecomposition temperature threshold can be met or exceeded within a timeframe that substantially inhibits stress waves from propagating beyondthe target volume, such that the ablation is substantially stressconfined to the target volume. The stress confinement conditions can bedetermined by the propagation speed of the stress waves and the geometryof the target volume. The resulting temporally and spatially uniformphase transition that occurs via spinodal decomposition within asubstantial majority of the target volume that creates a substantiallyconfined recoil stress so as to efficiently eject the volume, forexample without depositing substantial energy into the tissue adjacentto the target volume after the pulse.

Additional conditions that can be related to weakening the structuralintegrity of the target volume by liquefaction, for example liquefactionof collagen, optimized volume geometries and incident energy parametersensure a highly efficient removal process with substantially no affectto the surrounding region.

Silica based fiber optic waveguides are suitable for transmittingwavelengths with strong water absorption characteristics for flashtissue vaporization as described herein. Wavelengths greater than about2.3 um can exhibit strong bulk absorption in silica based fibers andwavelengths greater than 2.5 um can be impractical to use with silicabased fiber for ablation processes as described herein.

Many embodiments use light energy having wavelengths within a range fromabout 1.4 um to about 1.52 um and from about 1.86 um to about 2.5 um,and 2.5 microns may comprise a silica fiber limit. The wavelengths ofthese embodiments are strongly absorbed by water, are transmissible foruse through a silica based optical fiber waveguide and provide aninteraction depth of between approximately 70 um and approximately 700um, for example.

FIG. 1A shows the absorption characteristics of water and correspondingOPD across a broad range of wavelengths. The preferred wavelength rangesof 1.4 um to 1.52 um and 1.86 um to 2.5 um correspond to an OPD≦700 um.Additional embodiments include interaction depths between 70 um and 300um. Preferred systems have a penetration depth greater than about 50 um,to support interaction volumes and geometries sufficient for flashvaporization at reasonable rates.

FIG. 1B shows the absorption characteristics of water and correspondingOPD across a broad range of wavelengths. Wavelength ranges with OPDbetween 70 um and 300 um are from about 1.88 um to about 2.08 um andfrom about 2.34 um to about 2.5 um. As tissue may comprise substantialamounts of water, the water penetration depth can be used to determinetissue penetration and corresponding tissue ejection volume. A person ofordinary skill in the art can conduct experiments to determine tissuepenetration depths based on the teachings described herein. Non limitingexemplary wavelengths are 1.92 um, 1.94 um, 1.99 um and 2.01 um.Additional embodiments utilize a wavelength of approximately 1.94 um.The laser beams of embodiments with a wavelength of approximately 1.94um are strongly absorbed in water, are transmissible through a silicabased fiber and provide an interaction depth in the range of 80 um.

Flash vaporization can include delivering laser energy to tissue suchthat a substantial majority of the target volume of tissue reaches atemperature of approximately 300° C. or higher. By elevating the targettissue volume to at least 300° C., for example, the liquefactionthreshold of collagen can be reached as well as the threshold forspinodal decomposition of the target water chromophore. Various forms ofcollagen are present is many target tissues. By elevating thetemperature to the liquefaction threshold the structural integrity ofthe collagen can be at least significantly weakened. The weakenedcollagen structure reduces the energy used to eject the material,thereby significantly enhancing the efficiency of tissue removal. Byraising the preferred target chromophore, for example water (H₂O),within the tissue volume at least to its spinodal limit about 300° C. arelatively uniform phase change can occur within a substantial majorityof the target volume. The spinodal phase change is distinctly differentfrom nucleation and bubble growth mechanisms. At the spinodal thresholdlimit water becomes mechanically unstable and an ensuing rapid phasechange to vapor occurs with relative uniformity in the tissue volumecreating significant kinetic energy within the target volume.

A further aspect of flash tissue vaporization can include, for example,achieving at least an approximate temperature within the target volumeof 300° C. in a time sufficiently short such that the tissue adjacent tothe target volume has insufficient time to react substantially. Thus asubstantial majority of the energy is deposited in the target tissuevolume before any substantial absorption induced stress propagates fromand before substantial heat diffuses away from the target volume suchthat the stress propagation and heat diffusion are inhibitedsubstantially. This inhibition of the dissipation of stress propagationenergy and the inhibition of diffusion of heat energy can inhibit damageto tissue adjacent to the target volume after the target volume isejected.

The parametric constraints that can be used to describe laser beamparameters for the flash tissue vaporization are described by thefollowing equations, which establish a very complex parameter space.

$\begin{matrix}{\tau_{p} \leq \frac{1}{\mu_{a}v_{s}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

-   -   where τ_(p) is the pulse width (sec),    -   μ_(a)=absorption coefficient (cm⁻¹) or 1/fiber radius (cm)        whichever is shortest,    -   ν_(s)=velocity of sound (cm/sec)

Equation 1 corresponds to a condition where the pulse duration issufficiently short to prevent stress waves from propagating beyond thetarget volume relative to the shortest dimension of the target volume.For the purposes of flash vaporization substantial stress confinement,enabling tissue ablation via spinodal decomposition with negligibleadjacent tissue damage may be achieved with pulse durations up toapproximately 3 times the pulse duration indicated by equation 1.

$\begin{matrix}{\tau_{p} \leq \frac{1}{\mu_{a}^{2}\kappa}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

-   -   where τ_(p) is the pulse width (sec),    -   μ_(a)=absorption coefficient (cm⁻¹),    -   κ is thermal diffusivity (cm²/sec)

Equation 2 corresponds to a condition where the pulse duration issufficiently short to prevent heat from propagating beyond the targetvolume.

$\begin{matrix}{1 \geq \frac{{\kappa\tau}_{p}}{\delta^{2}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

-   -   where τ_(p) is the pulse width (sec),    -   κ is thermal diffusivity (cm²/sec),    -   δ is the chromophore size (cm²). For pure H₂O, eq3 is equivalent        to eq2 as δ=1/μ_(a)

Equation 3 corresponds to a condition where the pulse duration issufficiently short to prevent thermal propagation beyond the targetchromophore, where for example, the target chromophore represents smallvolumes of interstitial water dispersed within the collagen mesh work ofthe target tissue.

Equations 1-3 identify the upper limit of pulse durations related to thetissue laser interaction, suitable for flash tissue vaporization.

The temperature attained as a result of a laser pulse in tissue can becalculated from the following equation for pulses shorter than 1 μsec.

$\begin{matrix}{T = {\frac{\mu_{a}\phi}{C_{v}\rho}{\mathbb{e}}^{{- \mu_{a}}Z}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

-   -   where T=temperature (° C.),    -   Φ=Energy (J/cm²),    -   Cv=Where Cv is the isochoric specific heat (saturated liquid        heat capacity at constant volume) of the chromophore (H₂O) (J/g°        C.),    -   ρ=density (g/cm³)    -   and z=depth (cm)

Equation 4 indicates the required fluence to achieve a desiredtemperature at a depth in the target volume.

$\begin{matrix}{\phi = \frac{C_{v}T\;\rho}{\mu_{a}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

-   -   where T=temperature (° C.),    -   Φ=Energy (J/cm²),    -   C_(v)=specific heat (J/g° C.),    -   ρ=density (g/cm³)

Equation 5 indicates the appropriate fluence to reach the thresholdtemperature for spinodal decomposition of the target chromophore (H₂O).

Equations 1-5 may be used to determine, for a given wavelength andtarget tissue, the fluence required to reach 300° C. with substantiallythe entire target volume and to determine the maximum pulse durationsuitable for flash vaporization. For flash tissue vaporization the lowerpulse duration limit can, in part, be determined to prevent substantialplasma generation and to prevent damage to a waveguide delivering thepulse, like a silica based optical fiber.

Volumetric power density (VPD) can be re-cast to Equation 6;

$\begin{matrix}{{VPD} = {\frac{\mu_{a}E}{A_{r}t_{p}} = \frac{\mu_{a}E}{{\pi\omega}^{2}t_{p}}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$where:

-   -   E=energy (J),    -   μ_(a)=absorption coefficient (cm⁻¹),    -   A_(r)=area (cm²),    -   t_(p)=pulse width (sec) and    -   ω=radius of incident spot (mm) {{{cm??}}

Spinodal decomposition has a minimum VPD to substantially eliminateenergy loss due to bubble formation and/or cavitation. Experimentationsuggests a VPD of roughly 10¹⁰ W/cm³ or higher is sufficient to inducespinodal decomposition, in some instances typically with pulse durations≦200 ns. For stress confinement, shorter pulse lengths can be required.

Flash Vaporization may include a pulse width short enough for a giventarget tissue volume to inhibit substantial thermal or mechanical energywithin the interaction volume from propagating into the adjacent volumeduring the deposition of the light energy into the target tissue. It maybe advantageous for the pulse width to be long enough for a given peakirradiance and target tissue to substantially inhibit plasma formation.Propagation of thermal energy, mechanical energy and substantial plasmaformation may each introduce tissue removal inefficiencies that can leadto damage of the adjacent tissue. Pulse widths in the range of about 100ps to 1 us may be suitable for flash tissue vaporization. For example,pulse widths between 0.5 ns and 100 ns can be preferable for wavelengthstargeting water as a chromophore.

The parameters of Flash vaporization are related to the size of thetargeted tissue interaction volume. Larger interaction volumes mayrequire more laser energy to reach the spinodal and liquefaction limitswhile satisfying the above conditions so as to substantially preventthermal and/or kinetic energy from propagating into the tissue adjacentto the ablation site. As the above described pulse energy increases, thepulse duration may also increase in order to inhibit exceeding peakpower damage thresholds of the laser generator and/or the deliverysystem. The interaction volume range can be determined based on thelargest volume where flash vaporization can be achieved with a practicaland commercially viable laser and delivery system. For example using a1.94 um wavelength and targeting porcine kidney with approximately 70%water content with a 100 um core silica fiber in contact mode yields aninteraction volume of approximately 9×10⁻⁷ cm³. An interaction volumesize in the range of 10⁻⁸ cm³ to 10⁻⁴ cm³ can be used in manyembodiments. Many embodiments can use an interaction volume of 10⁻⁷ cm³to 10⁻⁵ cm³.

Flash vaporization can be related to the shape of the interactionvolume. The ratio of the interaction volume depth to the interactionvolume width may correspond to the efficiency in which the tissue isremoved including the ability to extract a substantially majority of theabsorbed laser energy with the ejected volume. The ejection of targettissue from the treatment site may comprise a mechanical process.Kinetic energy created by spinodal decomposition within the interactionvolume can drive the tissue material removal process. Optimizing theshape of the interaction volume can improve the efficiency of tissueremoval. Interaction volume shapes where the depth is substantiallylarger than the width may provide less efficient ejection of the targettissue, which can lead to residual mechanical or thermal effects ontissue adjacent to the target volume. Additionally, interaction volumeswhere the depth is substantially less than the width may lead toinefficient target tissue removal which may cause residual mechanical orthermal effects on the adjacent tissue. Depth and width ratios arerelated to the OPD of the wavelength used for a given target materialand the incident spot size delivered to the tissue surface.

FIG. 2 shows a representative interaction volume depth to width ratiofor several embodiments. One embodiment is a depth to width ratio ofapproximately 1:2, see FIG. 2a . This can be a preferred species becausethe efficiency of tissue ejection can be high, and the energy per pulseneeded to achieve tissue removal can be well within operating conditionsof a fiber optic delivery tool. Another embodiment is a depth to widthratio in a range between 1:4 to 2:1, see FIG. 2b . This rangeencompasses larger areas on the tissue surface, and requires largerenergy per pulse for the larger areas. These larger energy per pulserequirements can be more difficult to achieve with a given laser system.Another embodiment is a depth to width ratio in a range between 1:6 to2:1, see FIG. 2c . This more generic range of geometries includes evenlarger surface areas, requiring even larger energies per pulse.

The targeted tissue interaction volume size and/or shape can determinethe pulse energy to achieve Flash Vaporization. Too little energy perpulse may not drive the target chromophore to the spinodal limit and/ormay not provide sufficient kinetic energy to eject the material withinthe interaction volume. Too much energy per pulse may not be practicalto generate or deliver and can introduce inefficiencies in the tissueremoval process. In both cases, too little and too much per pulseenergy, residual mechanical and/or thermal affects on the adjacenttissue may occur. The threshold energy to achieve spinodal decompositioncan be calculated from equations 1-5.

The efficiency can be determined per equation 7.

$\begin{matrix}{\eta = {\frac{A\;\rho}{\mu_{a}E_{i}}{\ln( \frac{E_{i}}{E_{th}} )}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

-   -   where η=efficiency (gm/J),    -   μ_(a)=absorption coefficient (cm⁻¹),    -   A=spot size (cm²),    -   ρ=density (gm),    -   E_(i)=input energy (J) and    -   E_(th)=threshold energy for spinodal decomposition at the        surface (J)    -   And for optimum efficiency        E _(i) =E _(th) e yields E _(opt)    -   e is Euler's number=2.71828 (to five significant figures).

The ideal energy is related to the energy required to achieve spinodaldecomposition plus the additional energy to eject the target volume withoptimal efficiency. Energy exceeding E_(opt) is imparted to the ejectedmaterial, in this case water. Now as the target volume is not entirelywater and can contain significant amounts of collagen in differentorganizational structures, the energy exceeding E_(opt)-may be used toovercome the tensile strength of the tissue within the volume.

Many embodiments for flash vaporization include pulse energies withinthe range from about 100 uJ to about 100 mJ. Furthermore manyembodiments embodiment for flash tissue vaporization using water as thechromophore utilizes pulse energies from 500 uJ to 30 mJ. Specificembodiments for Flash Vaporization can use water as the chromophore anda wavelength near 1.94 μm and pulse energies from 1 mJ to 10 mJ.

The flash tissue vaporization process, in some instances, has thresholdfluences in the range of joules per centimeter squared.

FIG. 3 shows a laser system utilizing Flash Vaporization for tissueremoval during laparoscopic surgery. The patient 310 has an imagingsystem 320 inserted in the thoracic cavity. The imaging system 320 maybe a direct viewing type or it may have a camera with a video display330 such that the surgeon can view the inside of the thoracic cavity. Aninsertion device 340, such as an endoscope, with and a delivery system350 is also inserted into the thoracic cavity. The proximal end of thedelivery system 350 is attached to a laser system 360.

FIG. 4 shows the laser system of FIG. 3 for implementing a FlashVaporization based surgical device. The laser system has a userinterface 410 to adjust system parameters and to control the laserenergy emission. The user interface 410 is in communication with thecontroller 420. The controller operates the resonator 430 to provide theappropriate output selected via the user interface 410. The output oflaser energy from the resonator 430 is directed to a device coupler 440.The device coupler 440 directs the laser energy into a delivery system450. A representative delivery system 450 comprises a 100 um core silicafiber used in contact, or near contact, with the target tissue. Arepresentative non-contact delivery system 450 comprises a silica corefiber with a focusing element to generate a 100 um treatment spot about2 cm from the tip of the silica fiber. In other embodiments, fiber tipoptical components can be utilized for spot shaping and beam pointing.

FIG. 5 shows components of the resonator 430 for implementing flashtissue vaporization, having a gain medium 510, pump source 520,modulator 530 and at least two mirrors 540. Non limiting examples of thegain medium 510 include solid state, gas, liquid, semiconductor based orwaveguide based gain mediums. The gain medium 510 may be selected toprovide a specific wavelength or wavelength range that is desirable forinteraction with the target tissue. Non limiting examples of solid stategain medium 510 for the preferred wavelength range of 1.8 um to 2.5 umare Ho:YAG, Tm:YAG, Tm:YAP, Tm:GaV04 and Tm:YLF. A solid state gainmedium is an embodiment due to the ability to generate laser energy withhighly efficient pumping processes within wavelength ranges that maytarget chromophore present in a wide variety of tissue. Solid state gainmediums also enable small and low cost implementation. The lower costand size of solid state lasers are appealing to the surgeons andfacilities using the equipment. Non limiting examples of the pump source520 include a laser diode, arc lamp, flash lamp or electricalstimulation. A laser diode is a preferred pump source 520 offering a lowmaintenance requirements and an efficient means to pump the gain medium510. Furthermore an end pumping configuration may be employed to improvethe efficiency of the pumping process. A modulator 530 may be used toprovide pulsed laser energy and may be implemented intracavity orexternally. Non limiting examples of modulators 530 includeacousto-optic, electro optic, saturable absorbers or mechanical means.An embodiment may be an intracavity acousto-optic or electro opticmodulator. The electro-optic modulator may have further advantages whenthe laser resonator 430 produces polarized energy. The laser resonator430 preferably has two mirrors 540. One mirror reflected approximatelyall of the laser energy while the second mirror partially reflects thelaser energy serving as an output coupler to extract laser energy fromthe laser resonator. A two mirror resonator often reduces the laserresonator complexity and reduces the overall cost of the laser system.Additional laser resonator configurations with more than two mirrors mayalso be used. Optimizing the efficiency and simplicity of the laserresonator 430 is a factor in the commercial viability of a laser basedsurgical tool. A representative laser resonator configured for flashvaporization includes a gain medium 510 comprising Tm:YAP configured tolase efficiently at 1.94 um with a pump source 520 comprising a fibercoupled laser diode configured for end pumping the gain medium 510. Therepresentative laser resonator further includes a modulator 530comprising an acousto-optic Q-switch and two mirrors 540, onesubstantially reflecting all the light at 1.94 um and the secondpartially reflecting light at 1.94 um to function as an output coupler.

Thus, one species of a more generic class of laser systems capable ofuse for flash vaporization as described herein includes a Tm:YAP gainmedium 510 arranged to produce an output wavelength near 1940 nm,operating with an energy per pulse in the range of 1 to 10 mJ per pulsein pulse widths less than 100 nsec, with a beam delivery tool 350, 340,such as an endoscope with a fiber optic or other waveguide, arranged todeliver a spot size of 50 to 200 microns to a target tissue. Awavelength near 1940 nm has an optical penetration depth in water ofabout 80 microns. Because water is a primary component of most tissues,the penetration depth in tissue can be approximately the same. Using aspot size and a 80 micron penetration depth, one can determine thedimensions of an interaction volume within the tissue at the treatmentsite for a laser pulse. Using a pulse width less than 100 nsec, such asbetween 10 nsec and 50 nsec for a representative procedure, results in acondition of thermal and mechanical confinement of the energydissipation from the laser pulse, within that interaction volume. Usingan energy per pulse on the order of 0.5 to 40 mJ is sufficient in thisexample to generate greater than 10¹⁰ W/cm³ within the interactionvolume and raise the temperature of the water in the interaction volumeabove the spinodal limit, can cause confined spinodal decomposition ofthe water. The spinodal decomposition results in an instantaneous phasechange that creates substantial pressure in a range of about 200 bars to10 kBars within the interaction volume at the treatment site. Energy inthe pulse is translated via spinodal decomposition into kinetic energythat can eject the tissue without visible thermal damage to tissueadjacent to the ejected volume caused by thermal or acoustic wavesinduced by the ejection or the laser pulse. This effect is termed hereinFlash Vaporization. The laser system according to this species can beoperated with repetition rates from single shot to 2000 Hz, and becauseof the substantial volume of tissue ejected with each pulse, cuttingrates using Flash Vaporization that have not been possible using knownprior art techniques can be achieved.

Other species of laser systems within this more generic class includeslasers 430 operating in wavelengths that have similar opticalpenetration depths in tissue having water as a primary component,including wavelengths between 1400 and 1520 nm or between 1860 and 2500nm. Wavelengths in this range are also characterized by the fact thatthey are readily deliverable using silica waveguides on the order of 50to 200 microns in core diameter within the energy per pulse in the rangeof 0.5 to 40 mJ per pulse and pulse widths between about 10 nsec and 200nsec. A controller 420 and a visualization monitor 410 can be utilizedfor control of laser parameters and surgical procedures. In someembodiments, the controller 420 can be operated to control energy perpulse within a range from about 100 uJ to about 100 mJ. Furthermore manyembodiments embodiment for flash tissue vaporization using water as thechromophore utilizes pulse energies from 500 uJ to 40 mJ. Specificembodiments for Flash Vaporization can use water as the chromophore anda wavelength near 1.94 μm and pulse energies from 1 mJ to 10 mJ. Becauseof the availability and biocompatibility of silica waveguides, thesespecies of laser systems can be readily utilized in a wide variety ofendoscopic laser surgeries.

It is recognized that different tissue types may require differentparameters to achieve flash vaporization and eject substantially all ofthe material within the interaction volume. Thus a more generic class oflaser systems as described herein can be characterized by including alaser to generate a pulsed beam of light energy, each pulse of the beamto irradiate a volume of tissue and having a duration and an amount ofenergy to inhibit mechanical energy, or stress, and thermal energypropagation from the volume such that the volume of the tissue isejected with spinodal decomposition; and a controller coupled to thelaser to generate the pulsed light beam in response to commands from thecontroller. The system can be combined with an endoscopic delivery tool,including one or more optical fibers. Laser surgery based on flashvaporization can be performed within a complex parameter space describedin more detail below. The discovery of commercially feasible operatingconditions for lasers and delivery tools as described herein enables forthe first time, a new variety of “cold ablation” surgical techniques.

The spinodal decomposition process generates pressure within the targettissue volume. The pressure is generated, in part, when the chromophore,for example water, in the target volume reaches or exceeds the spinodalthreshold, thus initiating spinodal decomposition, on a time scalesufficient to substantially prevent propagation of thermal or mechanicalenergy beyond the target volume. The pressure generated ejects materialfrom the target site. The amount of pressure to adequately or optimallyeject substantially all of the target volume is, in part, dependent uponthe mechanical properties of the tissue itself. Various tissue typeshave different mechanical properties, in part, due to the collagenstructure of each tissue type. A comparison of skin to kidney is oneexample. Skin has a higher tensile strength than kidney Skins highertensile strength is, in part, due to skins function and the environmentskin is exposed too. Additionally skin typically has a lower watercontent than kidney tissue, resulting in a variation of the effectiveμ_(a) as compared to kidney when water is used as the chromophore. Thedifference in the effective μ_(a) and tensile strength may result indifferent pulse parameters within the flash vaporization regime toremove the two tissue types. The variation in pulse parameters, in part,reflects the different pressures needed to overcome the tensile strengthof each tissue type to eject substantially the entire volume of tissue,including the threshold pressure and the optimal pressure range. Bone isanother example where different pressures may be required to ejectsubstantially all of the tissue in the target volume. Bone typically hasa lower water content than soft tissue, which may affect the effectiveμ_(a) when water is the chromophore. The relevant mechanical propertiesof bone may be related to the force required to fracture bone within thetarget volume rather than pure tensile strength. The parameters forflash vaporization and the resulting pressure generated may be differentfor bone when compared to soft tissue.

The localized temperatures generated in the target volume during a flashvaporization event are near or exceed the liquefaction threshold forcollagen. At or above the liquefaction threshold for collagen thestructural integrity of the tissue may be compromised, weakening thecollagen structure. The weakened structures still exhibit variation inmechanical properties for different tissue types. Efficient removal ofspecific tissue types can be achieved, in part, by generating pressurein the target volume that is sufficient and/or optimal for tissueejection. Achieving flash vaporization with the ability to generate arange of pressures may be a factor in effectively targeting a widevariety of tissue types.

Equation 4, can be recast by substituting E/A_(r) for φ, yieldingequation 8, for pulses shorter than 1 usec.

$\begin{matrix}{T = \frac{\mu_{a}E\;{\mathbb{e}}^{{- \mu_{a}}Z}}{C_{v}\rho\; A_{r}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$where:

-   -   T=temperature (° C.),    -   E=energy (J),    -   A_(r)=area (cm²)    -   C_(v)=Where C_(v) is the isochoric specific heat (saturated        liquid heat capacity at constant volume) of the chromophore        (H₂O) (J/g° C.),    -   ρ=density (g/cm³) and    -   z=depth (cm)    -   μ_(a)=absorption coefficient (cm⁻¹),

The pressure generated in the target site can be calculated fromequation 9 for pulses shorter than 1 μsec.P=Aμ _(a) Γφe ^(−μ) ^(α) ^(z)  Equation 9where:

-   -   P=Pressure,

${A = \frac{1 - {\mathbb{e}}^{\tau}}{\tau}},{\tau = \frac{t_{\rho}}{t_{o}}},$

-   -   t_(ρ)=pulse width,

$t_{o} = {{{characteristic}\mspace{14mu}{pulse}\mspace{14mu}{width}} = \frac{1}{\mu_{a}v_{s}}}$

-   -   ν_(s)=sound velocity (cm·sec⁻¹)    -   Γ=Grüneisen parameter (dimensionless),

$\varphi = {{Fluence} = \frac{E}{A_{r}}}$

-   -   μ_(a)=absorption coefficient (cm⁻¹),    -   z=depth (cm)        In one embodiment the temperature and/or pressure throughout the        interaction volume are considered, specifically the temperature        and/or pressure at the optical penetration depth where

$z = {\frac{1}{\mu_{a}}.}$To achieve the spinodal decomposition threshold temperature at theoptical penetration depth

${z - \frac{1}{\mu_{a}}},$T can be recast as Equation 10,T=Te,  Equation 10where

-   -   T=temperature    -   e is Euler's number=2.71828

Now the temperature within the full optical penetration depth for eachpulse can be determined to meet or exceed the spinodal decompositionthreshold thus, in part, initiating flash vaporization throughout theinteraction volume.

Similarly to achieve, at least, the threshold pressure at the opticalpenetration depth

${z = \frac{1}{\mu_{a}}},$needed to eject a given target tissue, P can be recast as Equation 11,P=Pe,  Equation 11where:

-   -   P=pressure    -   e is Euler's number=2.71828

Now the pressure within the full optical penetration depth for eachpulse can be determined to meet or exceed the pressure threshold neededto eject substantially all the tissue throughout the interaction volume.

Equation 10, in part, determines the lower temperature limit for flashvaporization in H₂O throughout, substantially, the entire interactionvolume. However the pressure generated may not be enough to overcome themechanical strength of the target tissue. It may be necessary to adjustthe pulse parameters to achieve threshold or optimal pressure to ejectsubstantially all of the tissue within an interaction volume.Additionally each different target tissue type may have differentthreshold and/or optimal pressures for ejecting the respective tissues.If we re-cast the pressure equation to include the relevant parameterswe can see more easily which parameters will have the largest effect.

We have

$\tau = {{{\frac{t_{\rho}}{t_{o}}\&}\mspace{14mu} t_{o}} = \frac{1}{\mu_{a}v_{s}}}$thus τ=t_(ρ)μ_(a)ν_(s) and

$\varphi = \frac{E}{A_{r}}$where A_(r)=πω²So:

$\begin{matrix}{P = {\frac{1 - {\mathbb{e}}^{- {({t_{p}\mu_{a}v_{s}})}}}{t_{p}v_{s}} \cdot \frac{\Gamma\; E}{{\pi\omega}^{2}}}} & {{Equation}\mspace{14mu} 12}\end{matrix}$where

-   -   P=pressure    -   E=energy (J),    -   μ_(a)=absorption coefficient (cm⁻¹),    -   t_(p)=pulse width (sec),    -   ω=radius of incident spot (cm)    -   v_(s)=sound velocity (cm/sec)    -   Γ=Grüneisen parameter (dimensionless),

We notice immediately that P changes

exponentially as:

-   -   the pulse width    -   the sound velocity    -   the absorption coefficient

inversely with the square of the spot radius ω

linearly with energy

The velocity of sound is a property of the target chromophore and cannotbe readily changed for given type of target tissue. The wavelengthdirectly affects the absorption coefficient and may be usedindependently or in part to achieve a desired pressure. In oneembodiment where the wavelength remains constant, any one or combinationof pulse duration, energy per pulse and/or spot size may be changed toachieve a desired pressure for ejecting a specific target material. Eachparameter indicated in equation 12 may individually or in combination beadjusted to achieve a desired pressure. Within the multivariableparameter space that achieves a desired pressure, generating and/ordelivering a pulse with certain parameters may be impractical. Forexample a certain range of pulse energy and pulse durations may achievea desired pressure according to equation 12, but no laser source mayexist to achieve the particular pulse energy and pulse widthcombinations.

Similarly the ability, in practice, to deliver a pulse to a targettissue should be considered. For example, even in the absence of awaveguide, certain subsets of parameters within a parameter spaceachieving, at minimum, flash vaporization and tissue specific pressurethresholds may generate plasma at the tissue or in air which mayinterfere with the delivery of the pulse to tissue and thereforeultimately may not satisfy the conditions within the tissue volume forflash vaporization and/or pressure to eject the target tissue.

A waveguide, in some instances, may be selected such that a range ofpulse parameters can be successfully transmitted through the waveguideand subsequently adjusted, typically by focusing elements, to achieveflash vaporization with a pressure sufficient to eject, substantially,the entire target volume.

For many surgical applications it may be advantageous to use a waveguidewhere the waveguide core is roughly the same diameter as the treatmentspot size. One embodiment where the waveguide core and treatment spotsize are similar is when the waveguide is used in contact to or nearcontact to the target tissue.

Silica fibers are a dominate type of waveguide used to delivery laserenergy for endoscopic applications. Silica fibers are readily available,flexible, biocompatible and low cost. Silica fiber waveguides are apreferred embodiment for utilizing flash vaporization for many tissuecutting applications, including endoscopic procedures. The pulseparameters used to achieve flash vaporization and/or pressure sufficientto eject the target material have, in part, high peak power. High peakpower can damage silica based waveguides. A preferred embodiment istherefore a range of laser pulse parameters that both achieve flashvaporization with an appropriate pressure to eject the material for agiven target and can be reliably transmitted down a silica based fiberwithout catastrophic damage to the silica fiber. The theoretical bulkdamage limit for silica fiber is known across a broad range of pulsedurations, including a subset of pulse durations suitable for flashvaporization. In practice the theoretical limits have not been fullyachieved. Studies have shown the practical relationship between pulseenergy and pulse width follows equation 13E _(i) =ad ^(b) t _(min) ^(c)  Equation 13where:Where: a, b and c are coefficients that have been determinedexperimentally

a=3921.5

b=0.95

c=0.5

E_(i)=energy (J)

t_(min)=pulse width (sec)

d=fiber core diameter (cm)

For example, by knowing the target tissue type and selecting awavelength, essentially μ_(a) V_(s), C_(v), ρ can be determined. Then bysubstituting equation 13 into the relevant previous equations aparameter space, if it exists, for a given the tissue type, wavelengthand fiber damage threshold, can be determined such that condition forflash vaporization with sufficient pressure to eject the target materialcan be meet, including delivery with a silica fiber.

Cutting Rate Experiment

A flash tissue vaporization based laser system operating at a 1.94 umwavelength was built and used to conduct ex-vivo tissue cutting tests.The pulse energy used was approximately 3.5 mJ and was delivered througha silica based fiber optic waveguide, and the pulse repetition rate was400 Hz. The fiber tip was positioned in a mount and held in a fixedlocation. The movable test stand with a porcine kidney tissue sample wasmoved through the beam immediately in front of the fiber tip. Theapproximate length of the tissue sample was 2 cm with a thickness ofapproximately 2 mm. The flash vaporization system cut through the entiresample in 8 seconds. The system made a 2.5 mm long by 2 mm deep cut eachsecond. The volume of tissue removed per pulse was 6.28×10⁻⁷ cm³/pulse.This cutting rate is dramatically faster than prior art laser systems.For example an excimer laser system with similar pulse repetition ratesand incident spot size with the fluence optimized to operate in a modewithout adjacent thermal injury yields a rate of 3.14×10⁻⁹ cm³/pulse,200 times slower. Similarly a photospallation based Erbium YAG systemwith similar pulse repetition rates and incident spot size with thefluence optimized to operate in a mode without adjacent thermal injuryyields a volume removed per pulse of 1.57×10⁻⁸ cm³/pulse, 40 timesslower. A high power research oriented femtosecond system with similarpulse repetition rates and incident spot size with the fluence optimizedfor ablation without adjacent thermal injury yields a rate of 1.49×10⁻⁸cm³/pulse, over 40 times slower as well. FIG. 6 shows a bar chartcomparing cutting rates for various forms of resection withoutsubstantially any adjacent tissue injury. The photochemical,photospallation and ionization based systems do not have a suitablemeans for fiber delivery for typical surgical applications and aretypically limited to line of site delivery.

FIG. 7a is H&E stained histology of a cut made in ex-vivo porcine kidneywith the Flash Vaporization system. The cut was approximately 3 mm deepby 5 mm long and took approximately 3 seconds to perform with an averagepower of approximately 1.4 watts and a depth to width ratio of 1.2:1.The histology shows a clean cut with no apparent thermal injury to thetissue adjacent the cavity left by the ejected tissue. FIG. 7b is ahigher magnification image of the same tissue sample. The cut surfaceshows no apparent thermal injury. Flash Vaporization enables previouslyunobtainable high speed cutting rates for deeper incisions with noapparent thermal injury to the adjacent tissue. Also, no mechanicalinjury is seen, except on the microscopic scale that would notmaterially lengthen healing rates.

For some surgical procedures it may be desirable to remove a large massof tissue directly via Flash Vaporization rather than by excision. Forexample a surgical treatment for Benign Prostatic Hyperplasia mayinvolve removal of a large mass of prostate tissue. The removal ofprostate tissue can be achieved either via an excision style process ora mass tissue vaporization process, depending on the surgeon'spreference. Removal of tissue in the colon is another example whereremoval directly via Flash Vaporization may be advantageous. Sessilecolon tumors are embedded in the inner wall of the colon and may bedifficult to remove by excision. The ability to vaporize the tumor inlayers, without collateral damage, from the surface down to healthytissue may be advantageous.

Referring to equations 7 and 12 and the related equations describedherein there is at least one combination of parameters that provide theoptimal tissue ablation efficiency, maximum grams of tissue ablated perjoule. When operating at the optimal efficiency the maximum tissuevaporization rate can be achieved. The tensile strength of tissue typesvaries throughout the body thus it is evident that the optimalparameters required to remove the target tissue will vary. This isachieved by optimizing the pressure in the target volume. For examplethe pressure required for optimum vaporization of the dermis issignificantly higher than required for kidney

The maximum speed at which tissue can be vaporized via FlashVaporization corresponds to the optimal ablation efficiency. Therefore aproblem exists when the surgical procedure requires/desires a rate ofablation that is greater than the rate of ablation corresponding to thepeak ablation efficiency. To achieve ablation rates that exceed themaximum ablation rate described above, a novel delivery device with twoor more fiber optic waveguides may be used. As spot size increases, theenergy per pulse needed to achieve ejection by spinodal decompositionincreases significantly. This limits the size of a laser spot than canbe practically used in laser surgery applications.

Species of laser systems described herein are configured to removelarger volumes of tissue per unit time. Such species utilize laserscapable of producing outputs that are a multiple of the energy per pulseto be applied by each pulse. In such species, a delivery tool includingmultiple waveguides can be coupled to the laser system for delivery ofmultiple spots, preferably adjacent, of laser energy to the treatmentsite in parallel or in rapid sequence. As there is essentially noresidual energy in the tissue after ejection, the multiple spots aretreated essentially independently. High repetition rates and multiplespots can be used to achieve very high tissue removal rates.

A laser source may be capable of producing energy/power well beyond theamount required to achieve optimal ablation efficiency. Delivering alaser pulse to tissue with a fluence, for instance, greater than thepeak efficiency reduces the ablation efficiency and in some cases mayeven exceed the damage limits for a single fiber optic waveguide. Bydividing a laser pulse generated within the laser source and couplingthe pulse into multiple fibers each individual fiber can simultaneouslyreceive a portion of the pulse energy. Furthermore, by aligning theindividual fiber outputs to separate regions of the target tissue,typically adjacent to one another, each fiber can be configured suchthat the tissue at each fiber's individual treatment site is ablatedwith optimal ablation efficiency. Utilizing a laser system with multipledelivery fibers allows most or all of the available laser energygenerated by the laser source to be applied to tissue achieving FlashVaporization with optimal ablation efficiency. Multiple delivery fiberconfigurations increase the system's overall ablation rate to meetclinical needs where it is desirable to directly vaporize tissue fasterthan a single delivery fiber can achieve while maintaining FlashVaporization with optimal ablation efficiency.

For example it may be necessary to ablate a large brain tumor. The useof parallel pulse delivery to achieve high ablation rates can beunderstood with reference to the table shown in FIG. 8. Assume FlashVaporization at the optimal ablation efficiency is achieved with afluence of about 40 J/cm². As discussed increasing the fluence beyond 40J/cm² does not improve the ablation speed. An exemplary laser may becapable of generating a pulse within the Flash Vaporization parameterspace that well exceeds the 40 J/cm², for example a pulse that wouldequate to 160 J/cm², 4 times greater than what is required for optimalefficiency. By generating a pulse capable of supporting 160 J/cm² andthen dividing the pulse simultaneously and roughly equally among 4individual fibers, each fiber can delivery to tissue a fluence of 40J/cm², at optimal efficiency in parallel. When the fiber output ends arearranged to treat separate tissue regions, typically adjacent to oneanother, 4 times more tissue per pulse is removed while maintainingoptimal ablation efficiency.

The increased rate of tissue ablation achieved by utilizing multiplefibers has been described for an individual pulse, but is applicable toa sequence of pulses as well. For faster tissue ablation the multiplefibers are typically an integrated part of the delivery device with eachfiber output corresponding to separate treatment site, typicallyadjacent to one another. The number of fibers utilized is scalablewithin the limits described.

In the example of sessile colon polyps one could choose to use a fiberbundle arranged in a semi-circular fashion with five fibers, where thelaser can produce a pulse capable of generating a fluence five timeslarger than the single fiber optimal ablation efficiency fluence. Thepulse can be divided equally into 5 parts and then coupledsimultaneously into 5 individual fibers. For each laser pulse generated,5 times more tissue is removed than can be achieved with a single fiber.

Some tissue types have relatively high mechanical strength and requirehigher pressures to break apart the tissue matrix. A significantlimitation occurs if the Flash Vaporization parameters required toachieve the necessary pressure exceeds the power handling capabilitiesof a single silica fiber, as described in Equation 13. For example thecollagen of the dermal matrix is very strong and elastic. The pressurerequired to achieve Flash Vaporization in the dermis is higher than mostother soft tissues. For the dermis example, a reasonable assumption forthe fluence required for Flash Vaporization might be 200 J/cm² thishowever exceeds the capability of the fiber thus we are presented with achallenge. This problem can be readily addressed by utilizing multiplefibers arranged in a configuration such as that illustrated in FIG. 9.Multiple fibers 901, 902 configured so that the output overlap in asingle spot in the region 903 on the treatment site enable FlashVaporization pressures far in excess of that achieved by a single fiber.An exemplary laser would generate the requisite energy for optimizationof fluence at the target through two or more fibers. At or near thedistal end 904 of the device, the output beams of the fibers areorganized to overlap one another at the treatment site. For example eachfiber carries a pulse corresponding to the equivalent of 100 J/cm², wellbelow the fiber damage threshold. The fibers are configured such thatthe output beams overlap completely thus achieving 200 J/cm² at thetreatment site. Using multiple fibers enables Flash Vaporization tooccur with fiber delivery in tissues where single fiber deliver cannotachieve Flash Vaporization. One embodiment for the delivery device is tohave the fibers bent and/or angled near the output such that the outputbeams overlap completely at the treatment site, as illustrated in FIG.9. The delivery device may have slots, grooves or some physical means toalign and secure each fiber such that the output beams are overlapped atthe treatment site.

An alternative embodiment may employ focusing optics near the device tipSuch as shown in FIG. 10. In FIG. 10, a plurality of fibers 1001, 1002arranged in a manner such as might occur through an endoscope. At thedistal end, a lens 1003 is positioned to redirect the outputs of theplural fibers 1001, 1002 so that they overlap on a spot 1004 on thetreatment site on the tissue. Each fiber 1001, 1002 is positioned andsecured in the delivery device such that the output beam passes throughan optical element (e.g. lens 1003) that in part ensures the outputbeams of each fiber overlap at the treatment site. The optical elementmay be an integral part of the fiber tip such as a shaped tip, gradedindex fiber tip, tapered tip or other bonded, fused, attached ormodified tips contributing to directing light. Additionally the opticalelement may be a single lens, individual lenses for each fiber, or anyother configuration of optical element(s) that ensures overlap at thetreatment site for each fiber output as illustrated in FIG. 10.

Achieving higher pressures during Flash Vaporization via therecombination of multiple fiber outputs can employ two or more fibers,one or more optical elements and/or numerous mechanical positioning andmounting configurations.

FIG. 11a illustrates a linear arrangement of fiber tips 1101, 1102,1103, 1104 that can be utilized in a delivery tool, to provide forincreased rate of cutting. The fiber tips 1101, 1102, 1103, 1104 in thisexample are positioned in a line, and adjacent to one another. Utilizingmultiple fibers for faster tissue ablation additionally enablescustomized tip geometries that can be shaped to accommodate the needs ofa given procedure.

When a delivery device is configured in a line and is moved such thatthe line is along the cut direction represented by arrow 1105, see FIG.11b , a scalpel like cutting effect is achieved. The direction of motionmimics a standard scalpel, enabling cuts to be made faster thanachievable with a single fiber.

Alternatively the fiber tips can be staggering to provide an angle withrespect to the tissue. FIG. 12 is a perspective view of a four fiberdelivery tool 1200 in which the fiber tips 1201 are arranged in astaggered configuration, where a first fiber extends distally relativeto the laser source by a small stagger relative to a second fiber, andso on in a stairstep configuration through all of the fibers in theline. The sizes of the stairstep can be equal or varied as suits theneeds of a particular arrangement. Representative sizes of the stairstepcan be on the same order as the diameter of the fibers or smaller, forexample. In the configuration of FIG. 12, the direction and angle of thedevice handle can mimic a scalpel 1202 ergonomically.

With a linear device tip configuration, mass vaporization can beachieved be moving the device in the direction perpendicular to thefiber arrangement. As represented in FIG. 13, by the arrow 1301, alinear device tip including a plurality of fibers, such as fibers1101-1104, can be moved in a direction orthogonal to the line of fibers.

When this configuration is moved across a target tissue it providesrapid ablation of a strip width equal to the width of the fiberarrangement. FIG. 14a illustrates an arrangement of fiber tips 1401-1407in a semicircular shape, as an alternative beam delivery tool. FIG. 14billustrates yet another alternative, in which three fiber tips 1408-1410are arranged in a nonlinear triplet. FIG. 14c illustrates a tightlypacked cluster of fiber tips, where six fibers 1411-1416 surround acentral fiber 1417.

Each tip configuration can be chosen to accommodate the clinical need.The treatment spots created by each individual fiber would be unique andin general adjacent to one another. For example to debulk a sessilecolon polyp a linear or curved arrangement may be employed such that thetip is drug across the tissue achieving vaporization over a largesurface area per pass than a single fiber, as illustrated generally inFIGS. 15a and 15 b.

For vaporization of tumors with a generally spherical shape, amulti-fiber tip 1601 may be used where the central portion 1602protrudes further into the tissue than the fiber tips (e.g. 1603, 1604)closer to the edges, as illustrated in FIG. 16.

For vaporizing tissue along the longitudinal axis of a generallycylindrical shape, such as in transurethral prostate resection, a tip1701 with fiber tips arranged in a curved configuration can be used,with a near right angle bend 1702 employed to direct energy laterally,and quickly vaporize a large mass of tissue, as shown in FIG. 17.

For removal of pacemaker leads a device that can be inserted coaxiallywith the wire lead is desirable. FIG. 18 shows a delivery device with acircular fiber arrangement 1801, with an open center 1802, which mayenable Flash Vaporization of the tissue adhered to the wire's outersurface, allowing the lead to be detached and removed.

A tight circular formation can be used when mass tissue vaporization isneeded and a painting motion over the diseased tissue is desirable.Using a painting motion the surgeon can control the depth ofvaporization by hand to achieve a desired margin, for example toefficiently resect a tumor with large variations in depth, as shown inFIG. 14 c.

In order to use multiple delivery fibers a means to direct all or aportion of the laser energy into two or more fibers is necessary.Passive components such as partial reflectors are non-limiting examplesof components that may be used to direct predetermined portions of thelaser beam into multiple directions. Active components such as rotatingmirrors are non-limiting examples of active means to direct portions ofthe laser beam in multiple directions. The beam path may be serial,parallel or any permutation of serial and parallel. The percentage oflight from the source that is transmitted and ultimately coupled to eachfiber may be static as determined by a beam directing component.Alternatively active components such as shutters, modulators,attenuators and the like may be used to control when and what percentageof the source light is coupled into any individual fiber.

For example a 4 fiber arrangement such as shown in FIG. 19, includingfibers 1900-1903 may be desirable for large volume tissue ablation. Thisarrangement can be used with a system like that of FIG. 20. In thisexample the laser source 2000 generates a pulse that can be dividedequally into 4 fibers while providing tissue ablation via FlashVaporization for each fiber at adjacent tissue sites. In the arrangementof FIG. 20, the laser source 2000 generated output that intersect beamsplitter 2001, which passes 25% of the energy through a fiber couplinglens into fiber 1900. The remaining 75% of the energy is directed pastthe shutter 2002 to a second beam splitter, which deflects one third ofthe remaining 75% (i.e. 25% of the original energy) through a fibercoupling lens into the fiber 1901. The remaining 50% of the originalenergy is directed to a third beam splitter 2004, which deflects onehalf of the remaining 50% (i.e. 25% of the original energy) through afiber coupling lens into the fiber 1902. The final 25% of the originalenergy is directed to the reflector 2005, through a fiber coupling lensinto the fiber 1903. When mass tissue vaporization is required theshutter 2002 is open and all four fibers will Flash Vaporize the targettissue. When precise cutting is needed the shutter 2002 is closed andonly one fiber receives a portion of the source pulse to Flash Vaporizethe target tissue. Of course other arrangements of shutters and beamsplitters can be utilized to implement a desired control sequence.

For embodiments with two or more laser sources similar fiber couplingtechniques can be used.

One embodiment utilizes one or more fibers of a delivery device forFlash Vaporization and one or more different fibers of the same devicefor coagulation purposes. This is represented schematically in FIG. 21,in which a first fiber 2100 is used for flash vaporization, and a secondfiber 2101 is used for delivering energy for coagulation. In someinstances the coagulation fiber(s) may have different core sizes thanthe Flash Vaporization fiber(s) or than each other. The coagulationfiber(s) tip may be flush with the Flash Vaporization fiber tip(s) orpositioned back from the Flash Vaporization fiber tip(s). One advantageof an offset coagulation fiber tip is that the laser energy transmitteddown the coagulation fiber may have similar or identical energy, pulseduration, wavelength characteristics to the laser energy transmitteddown the Flash Vaporization fiber but since the coagulation fiber isposition such that the interaction volume exceeds that required forFlash Vaporization the delivered energy results in coagulation. It mayalso be desirable to heat tissue over larger area than the FlashVaporization interaction area, again offsetting the coagulation fibercan help achieve the larger coagulation area.

Regardless of the fiber configurations the coagulation fiber(s) maytransmit different energy, pulse duration, repetition rate and/orwavelengths than are used with Flash Vaporization fibers(s) to provide ameans for coagulation. In some cases the coagulation fiber(s) may bedisabled while Flash Vaporization is occurring or vice versa.Alternatively the Flash Vaporization and coagulation fibers may beenabled simultaneously.

Another embodiment is to change the operating mode of the laser betweenFlash Vaporization and coagulation modes while directing the laserenergy down any combination of fibers for a given multi-fiber device.For example the laser system may produce a repetitive sequence ofseveral Flash Vaporization pulses followed by a period of continuouswave energy. In the example of a tightly packed circular multi-fiber tipthe Flash Vaporization/Coagulation sequence can be directed down eachfiber roughly equally.

Any of the above mentioned multi-fiber delivery device tip arrangementsmay actively control the transmission through each individual fiber. Acircular arrangement as described for use with a painting motion canremove tissue very rapidly. If a surgeon needed to make small precisecuts occasionally during this mass ablation process the FlashVaporization pulse energy can be directed only down 1 of the fibers, forexample the center fiber, as represented in FIG. 22 by darkening theexterior fibers in the cluster. This exemplary deliver device and lasersystem can maintain the precise cutting capability of a single fiber andhave the rapid mass tissue ablation capability enabled by using multiplefibers within the Flash Vaporization parameter space. An additionalembodiment is a scalpel like device configuration with a broad range ofcutting rates, as illustrated schematically by the light and dark fibertips in FIGS. 23a, 23b, 23c and 23d . The slowest cutting ratescorrespond to only 1 fiber being enabled to deliver Flash Vaporizationpulses. Slow cutting rates may be achieved by enabling 2 fibers. Fastercutting rates may be achievable by enabling 3 fibers. The fastestcutting rates may be achieved with all 4 fibers.

Virtually any combination of enabled/disabled fibers within anarrangement can be chosen and in some cases dynamically controlled viaan user interface or even within a system's internal programming.

Utilizing multiple fibers greatly expands the clinical capabilities of aFlash Vaporization tissue removal system.

FIG. 24 is a graph of pressure (kBar) versus pulse width (nsec) forenergy of 5 mJ per pulse at a representative wavelength of about 1940nm. In the graph, trace 2401 corresponds to the results using a 50μ corediameter fiber. Trace 2402 corresponds to a 100μ core diameter fiber.Trace 2403 corresponds to a 150μ core diameter fiber. Trace 2404corresponds to a 200μ core diameter fiber. Greater pressures areachievable using smaller fibers, because of the volumetric power densityis higher. However, the ability of a fiber to carry sufficient energyper pulse can limit the pulse with usable. For example, a 50μ fiber maynot be able to carry 5 mJ at pulse widths of less than 40 nsec. Forperspective, it is found that pressures in the range of about 200 Bar toabout 10 kBar are desirable for most types of tissue. It can be seenfrom trace 2402 therefore that a 100 μm core diameter fiber can bereadily usable over the desired range using less than 10 mJ per pulse.

FIG. 25 is a graph of pressure (kBar) versus energy (mJ) for a pulsewidth of 30 nsec. In the graph, trace 2501 corresponds to the resultsusing a 50μ core diameter fiber. Trace 2502 corresponds to a 100μ corediameter fiber. Trace 2503 corresponds to a 150μ core diameter fiber.Trace 2504 corresponds to a 200μ core diameter fiber. Each trace2501-2504 terminates at about the limit in millijoules per pulse forthat pulse width imposed by the fiber core diameter. Again, this plotillustrates that a 100μ fiber is readily usable over the desired rangeof pressure. It can be noted that as the pulse width increases from theexample here of 30 ns, the amount of allowable energy transmittedthrough a fiber increases significantly more slowly than the pulsewidth.

FIG. 26 is a graph of the maximum allowable energy (mJ) through a fiberas a function of pulse width (nsec). In the graph, trace 2601corresponds to the results using a 50μ core diameter fiber. Trace 2602corresponds to a 100μ core diameter fiber. Trace 2603 corresponds to a150μ core diameter fiber. Trace 2604 corresponds to a 200μ core diameterfiber. These plots illustrate that for a given fiber core diameter, oneneeds to increase the pulse width from about 10 ns to about 100 ns toenable delivery of only three times the maximum energy per pulse. Also,since flash vaporization sets a maximum pulse length on the order of 100ns for this example, the amount of energy per pulse deliverable throughfiber is significantly limited. The plot illustrates that a fiber corediameter of about 100μ is a suitable delivery tool across the preferredrange.

FIG. 27 is a plot energy (mJ) per pulse for 30 ns pulse, versus fibercore diameter (microns). Trace 2701 shows the threshold energy forinducing spinodal decomposition. Trace 2702 shows the maximum energydeliverable in a 30 ns pulse for a given fiber core diameter. The regionbetween the traces 2701 and 2702 shows a suitable working parameterspace for flash vaporization.

Embodiments of the present invention can utilize flash vaporization toquickly and efficiently cut and resect one or more of many tissue types,for example without substantial thermal or mechanical damage to thetissue adjacent to the cut into the tissue. Removing tissue withdecreased damage to the adjacent tissue regions can improve clinicaloutcomes, reduce the risk of adverse events and expedite the patient'srecovery. A laser can produce pulses of light energy to eject a volumeof the tissue, and the energy can be delivered to a treatment sitethrough a waveguide, such as a fiber optic waveguide. The incident laserenergy can be absorbed within a volume of the target tissue with atissue penetration depth and pulse duration such that the propagation ofthe energy from the tissue volume is inhibited and such that the targetchromophore within the volume reaches the spinodal decompositionthreshold and subsequently ejects the volume, for example withoutsubstantial damage to tissue adjacent the ejected volume.

In a first aspect, embodiments provide a method of removing tissue withlight energy. A pulsed beam of the light energy is directed toward thetissue. Each pulse irradiates a volume of tissue and has a duration andan amount of energy to inhibit stress and thermal energy propagationfrom the volume such that the volume of the tissue is ejected via themechanism of spinodal decomposition.

In many embodiments a pulsed beam of the light energy is directed towardthe tissue. Each pulse irradiates a volume of tissue with a given energyand a duration short enough that most if not substantially all of thestress and thermal energy is confined within the volume and the tissueis ejected via the mechanism of spinodal decomposition. Furthermoreenergy, pulse duration and additional parameters described herein areselected for a given target tissue to achieve spinodal decompositionwith substantial stress and thermal confinement, generating sufficientand/or optimal pressure within the target tissue to exceed themechanical strength, tensile strength is some instances, of the targettissue such that substantially all the tissue within the interactionvolume is ejected. Additionally the sufficient and/or optimal pressuremay vary depending on the target material's characteristics.

In many embodiments, the target volume is heated with substantial stressand thermal confinement above a threshold of spinodal decomposition to atemperature of at least about 300 degrees C., such that a temporally andspatially uniform phase transition occurs within the volume to eject thevolume without substantial energy deposition to tissue adjacent to thetarget volume. The temporally and spatially uniform phase transitionwithin the entire target volume can create a confined recoil stress soas to efficiently remove the volume without depositing substantialenergy in the surrounding region.

In many embodiments, the volume is ejected without substantial stresspropagation of mechanical energy from the volume and without substantialthermal diffusion of thermal energy from the volume. The pulse durationmay correspond to a dimension across the volume and a stress wavepropagation time across the volume so as to substantially inhibitpropagation of a stress wave from the volume.

Flash vaporization can be induced, given an optical penetration depth,OPD, as a function of the wavelength of the beam and the absorptioncoefficient for that wavelength in a primary chromophore such as waterin the tissue, using a cross sectional dimension of the beam at thetarget tissue sized to define an interaction volume such that onspinodal decomposition of the chromophore, the resulting pressureinduced kinetic energy, causes ejection of remaining tissue in thetarget volume. Also, as a result of the size of the volume of tissueejected by each pulse and the pulse repetition rates applied, the rateof cutting accomplished using flash vaporization can be comparable tothat possible when making fine incisions using a scalpel. Flashvaporization can be induced using a pulse duration short enough tomaintain substantially stress confined interaction with the tissue, suchthat damage to surrounding tissue caused by tearing or other stress isnot visible or not significant in terms of its effect on healing rates.Also, flash vaporization can be induced using a pulse duration shortenough to maintain substantially thermally confined interaction with thetissue in the target volume, such that damage to surrounding tissuecaused by heat is not visible or not significant in terms of its effecton healing rates. Flash vaporization can be induced using a wavelengthsuitable for delivery using silica optical fibers, or other flexiblewaveguides, while the pulse duration is long enough to allow deliverythrough the waveguide with only minimal damage or wear, so that fiberdelivery is practical and preferred.

In many embodiments, each volume is irradiated with each pulse to definea depth and cross-section size of the volume based on the tissue's OPD,the pulse duration and the cross-section beam size such that the volumeis substantially stress confined and substantially thermally confined toeject the tissue via the mechanism of spinodal decomposition. The lightenergy can be transmitted through an optical fiber, and the light energymay comprise a wavelength from about 1.4 microns to 1.52 microns or fromabout 1.86 to about 2.5 microns to define the volume based substantiallyon water absorption.

Representative durations of each pulse can be within a range from about100 picoseconds to about 1 micro second. More typical pulse durations ofeach pulse can be within a range from about 500 picoseconds to about 200nanoseconds.

In many embodiments, the volume ablated with each pulse is within arange from about 1×10⁻⁸ cm³ to about 1×10⁻⁵ cm³. In alternativeembodiments the volume ablated with each pulse can be within a rangefrom about 1×10⁻⁷ cm³ to about 1×10⁻⁶ cm³.

In many embodiments, the volume corresponds to a depth and a widthejected with each pulse and a ratio of the depth to the width is withina range from about 2:1 to 1:6. The volume may correspond to a depth anda width ejected with each pulse and a ratio of the depth to the widthcan be within a range from about 2:1 to about 1:4, as in the case of1940 nm wavelength in tissue having water as a primary chromophoredelivered via fibers having core diameters of 50 to 200 um in contactwith, or nearly so, the target tissue.

In many embodiments, the amount of energy of each pulse is within arange from about 100 micro Joules to about 100 milliJoules. Inalternative embodiments the amount of energy of each pulse can be withina range from about 500 micro Joules to about 30 milliJoules. Inadditional embodiments the amount of energy of each pulse can be withina range from about 1 milliJoule to about 10 milliJoules.

In many embodiments, the tissue comprises collagen and wherein thecollagen may reach or exceed the liquefaction threshold with each pulseof the light energy.

In many embodiments, the tissue comprises one or more of vascular softtissue, cartilage or bone.

In many embodiments, an elongated incision having a length and a depthis formed in the tissue with the light energy, and the length and thewidth correspond to an area of the incision into the tissue and whereintissue removal rate is at least about 10⁻⁸ cm³/pulse up to 10⁻⁴cm³/pulse. Pulse repetition rates from single shot to 2000 Hz arerepresentative. For fine or microscopic cutting, repetition rates lessthan 100 Hz may be used, including single pulse triggering to causepulse by pulse operation.

In many embodiments, the light energy is transmitted through at leastone optical fiber with an energy transmission efficiency of at leastabout 80%.

In another aspect, embodiments provide an apparatus to treat tissue. Alaser generates a pulsed beam of light energy comprising a plurality oflight energy pulses. Each pulse irradiates a volume of tissue and has aduration and an amount of energy so as to substantially inhibit stressand thermal energy propagation from the volume such that the volume ofthe tissue is ejected via the mechanism of spinodal decomposition. Acontroller is coupled to the laser to generate the pulsed light beam inresponse to commands from the controller.

In many embodiments, at least one optical fiber is coupled to the laser,and the plurality of pulses of the pulsed beam transmitted through thefiber to the tissue such that each pulse transmitted through the fiberis capable of irradiating a volume of tissue and has a duration and anamount of energy so as to substantially inhibit stress and thermalenergy propagation from the volume such that the volume of the tissue isejected via the mechanism of spinodal decomposition.

Flash vaporization is a unique and clinically important new capability.As described herein different target tissue may have differentmechanical properties, requiring different amounts of threshold and/oroptimal pressure to be generated within the treatment volume to ejectsubstantially all of the material. It is desirable to provide surgeonswith a cutting system that enables flash vaporization with efficienttissue ejection across a variety of tissue types. The versatility to cuta diverse variety of tissue types without substantially any thermal ormechanical damage to the tissue adjacent to the target volume enablessurgeons provide better outcomes, less risk and shorter recovery periodsfor their patients.

Although specific reference is made to flash tissue vaporization, theflash vaporization as described herein can be used to flash vaporizemany types of material, such as non-tissue material comprising water,for example.

A process is described including selecting a pressure to match tissuetypes; and adjusting the pressure to at least eject substantially allthe target volume, wherein different tissue types have differentthreshold pressures. Also, a process is described including adjustingpressure with constrained ranges of wavelength, pulse duration, energyper pulse, and spot size parameters to at least achieve an ejectionthreshold for the target tissue.

Embodiments of the present invention provide improved methods andapparatus so as to provide versatile and effective tissue removal. Asurgical laser system may comprise dynamic pulsing control of pulsewidth and intensity coupled to a user interface, such that the user canselect a broad range of tissue treatment. For example, the system mayallow a user such as a surgeon to select a target tissue responseranging from cold ablation, including flash vaporization, through tocoagulation. The target tissue response may comprise a user selectableresponse desired by the surgeon based on visual feedback from a surgicalimage such as an endoscopic image. For example, the tissue response canrange from cold ablation, including flash vaporization, withoutsubstantial coagulation to coagulation with minimal ablation. The coldablation, including flash vaporization, may comprise cutting soft orhard tissue with short pulses having a duration of no more than about500 ns, for example, such that the tissue may be cut without substantialthermal deposition and without substantial thermal damage to theunderlying tissue of the ablation site. The laser beam may comprise awavelength absorbed substantially with the tissue, for example such thata majority of the energy of the laser beam is absorbed within about 100microns of tissue penetration. For example, the laser beam may comprisea wavelength within a range from about 1.8 to about 2.2 μm, such thatthe energy of the beam can substantially ablate the tissue with shortpulses having a duration of no more than about 500 ns and such that theenergy of the laser beam can induce thermal damage to the tissue with acontinuous wave or repetitive pulses with a period less than about 2 ms.The thermal damage of the tissue may comprise substantial coagulationwith a continuous wave or repetitive pulses with a period less thanabout 2 ms, for example, such that a substantial majority of the energyincident on the tissue results in thermal deposition and coagulation ofthe tissue with minimal tissue ablation. The user may selectintermediate treatment modes where the corresponding tissue response issuch that tissue is cut with moderate thermal deposition, for example.This substantial breadth of the targeted tissue response from coldablation, including flash vaporization, to coagulation can be achieved,for example by dynamically varying the pump source and q-switch pulseparameters. The pump source and q-switch parameters can be variedindependently, together, or combinations thereof, for a selectedexposure setting. For example the pump source parameters of the lasergain medium and q-switch parameters can be varied together when thetissue is treated, so as to provide the wide range of user selectabletreatment.

The system may comprise a small core waveguide, for example less thanabout 100 μm, so as to provide a very efficient cutting and coagulation,and to provide substantial accessibility to treatment sites withdecreased invasiveness, for example endoscopic procedures to the sinuscavity accessed through a nose of the patient. The waveguide can becoupled to the laser such that the tissue at the treatment site istreated with the laser beam output in accordance with the targetedtissue response, for example one or more of cold ablation, includingflash vaporization, ablation with coagulation, or coagulation withoutsubstantial ablation. As the user can change the targeted tissueresponse during treatment, for example in response to endoscopic imagesshown on a display, many surgeries can be performed with decreasedinvasiveness and improved results.

The user selectable cutting or coagulation of tissue can be achieved inmany ways, for example, by pulsing the laser output beam in variabletiming patterns and combinations. The pulses can be generated by pulsingthe pump source, pulsing the laser beam with the q-switch, or pulsingboth. The laser system may include a pump source such as laser diodescoupled to a gain medium, a q-switch, mirrors sufficient to create aresonate cavity with the gain medium disposed therein, optics to focusthe output laser beam into a delivery device such as a waveguide, acontroller with a tangible medium, and an user interface. The waveguidemay comprise an optical fiber coupled to the laser output so as todirect the laser output from the laser source to the treatment site. Thesystem may further comprise an insertion device that at least one ofhouses or holds the waveguide for insertion of the waveguide into thebody. The insertion device may be shaped to accommodate access andplacement of the waveguide for performing specific surgical procedures,such as surgery of the sinus cavity.

Embodiments of the present invention provide improved methods andapparatus so as to provide versatile and effective tissue removal. Thesurgical laser system as described herein can be used with many surgicalprocedures and can be used to access many surgical locations of apatient, for example internal surgical locations. The surgical lasersystem has a user interface that allows the user to select a treatmentbased on a desired tissue response such as cold ablation, includingflash vaporization, coagulation or ablation with intermediate levels ofthermal damage. The laser system comprises circuitry coupled to the userinterface and the laser, such that the circuitry can adjust the lasertreatment parameters based on the tissue response identified by theuser. The laser treatment parameters adjusted with the circuitry caninclude one or more of the pulse duration or exposure duration withcontinuous wave output, the output beam intensity, the intensity of thepumping of the gain medium, or pulsing of the gain medium, for example.The user can view an image of the tissue site, for example with anendoscope comprising viewing optics and the tissue treatment waveguide,and the user can select the desired tissue response based on theendoscopic images, such that the tissue can be cut with cold ablation,including flash vaporization, coagulated, or cut with a desired level ofthermal damage as targeted by the user.

Although many of the figures as shown herein show laser beam pulseamplitudes with rectangles, based on the teachings described herein oneof ordinary skill in the art will recognize that the pulsed laser beamsof the embodiments described herein may comprise laser beam pulseshaving an output with a Lorentian or other distribution or profile overtime such that the pulse duration may encompass a full width halfmaximum of the laser beam.

FIG. 28A shows the disclosed invention being used for sinus surgery. Thepatient 2870 has an imaging system 2880 inserted in a nostril. Theimaging system 2880 may be a direct viewing type or it may have a camerawith a video display 2860 such that the surgeon can view the inside ofthe sinus cavity. An insertion device 2990 with an insertion devicehandle 3000 and a waveguide 2980 is also inserted into the sinus cavity.The proximal end of the waveguide 2980 is attached to a laser system2890 with an user interface 2960. The user can adjust the user interfacesetting to achieve the desired clinical effect. In one approach, flashvaporization as described above is utilized to remove tissue in thesinus cavity. The user interface 2960 also provides a means to activatethe laser system to delivery energy to the treatment site via thewaveguide 2980 and insertion device 2990.

FIG. 28B shows the laser system of FIG. 28A for implementing a versatileand effective surgical tool with enhanced clinical capabilities. Thelaser system has a gain medium 2900 and q-switch 2910 disposed betweenleast two mirrors 2920 aligned to form a resonant cavity. A pump source2930 provides energy to excite the gain medium 2900. A controller 2940with a tangible medium 2950 may communicate or operate the pump source2930 and the q-switch 2910. A user interface 2960 communicates with thecontroller 2940. The resulting laser energy passes through couplingoptics 2970 to be coupled into a waveguide 2980. The waveguide 2980passes through an insertion device 2990 used to insert the deliverysystem into a body. The insertion device may have a insertion devicehandle 3000 for the surgeon to hold and manipulate the insertion device2990. In many embodiments, the laser system has a controllable pumpsource 2930 capable of generating a pulsed laser output beam. Somenon-limiting examples of controllable pump sources include: flash lamp,arc lamp, hybrid lamp, diode laser, solid state laser, gas laser, dyelaser, fiber laser and direct electrical stimulation. The pump source2930 may in turn have a power source to operate it. The power source maybe controllable to provide pulsed power to operate the pump source 2930in a pulsed mode. Any means to control at least one of pulse amplitude,pulse duration or pulse period, preferably all three can be sufficient.Dynamic pulse control may be in the form of one set of pulse parameters,fixed during an exposure, for a given user setting and alternative setsof pulse parameters, fixed during the exposure, for different usersettings. Additionally dynamic pulse control may be in the form of oneor all pulse parameters changing during an exposure in a specified wayfor a given user setting, where each individual user setting may havedifferent parameter changes during an exposure.

FIG. 29A shows an example output waveform of the laser as in FIG. 28Bwith a series of laser beam pulses of substantially fixed pulse durationfor thermal deposition to tissue with relatively less tissue cutting.

FIG. 29B shows an example output waveform of the laser as in FIG. 28Bwith a series of laser beam pulses of fixed duration to cut whiledepositing less heat than the pulse series of FIG. 29A. The user mayselect between these two pulse structures, or many similar embodiments,depending on the surgical need. Some embodiments allow controlledvariations of the pulse parameters for each individual pulse of amulti-pulse exposure. The pulse parameters may include: amplitude,duration and period.

FIG. 30A shows a non-limiting example output waveform of the laser as inFIG. 28B with a linearly increasing stair case pulse amplitude with anincreasing pump period and increasing pump pulse duration. Alternativelythis pulse structure could have a decreasing stair case or pulse periodor pulse duration or inter-mixed combination of increasing, decreasingor static parameters. Also the rate of change from pulse to pulse couldbe non-linear for any one or up to all of these parameters.

FIG. 30b shows an example output waveform of the laser as in FIG. 28Bwith a decreasing pulse period and decreasing pulse duration in aperiodic cycle. Alternatively the period or pulse duration may beincreasing or combinations of increases and decreases. Also the patternperiod could be shorter or longer with more or less substructure pulses.The amplitudes may be varied as well. Pulse control allows the tissueinteraction to be customized to concurrently control the cutting rateand amount of thermal damage incurred on the remaining tissue. There aremany pulse parameter permutations, both simple and complex that offer aclinical significance for surgery. Pulse control on an individual pulsebasis during a multi-pulse exposure allows further refinement andcontrol of cutting and coagulation.

FIG. 30C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a pump pulse mode to maintain arelatively constant cutting rate with more coagulation near thebeginning of the exposure than the end of the exposure.

For example when a surgeon intends to maintain a relatively constantcutting rate but create deeper coagulation near the beginning of theexposure than the end, a non-linear decrease in pulse durations whileincreasing the amplitude during a multi-pulse exposure can begin with agreater deposition of heat into the tissue and then taper to less heatdeposition, combined with a decrease in the period a steady cutting ratecould be maintained, so as to provide enough heat to establishhemostasis and then proceed to cut without continuing to depositexcessive amounts a heat into the remaining tissue, as shown in FIG.30C.

FIG. 30D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a pump pulse mode to create a relativelyuniform coagulation zone around the contour of the cut region.

For example, when a surgeon intends to cut tissue while leaving arelatively uniform coagulation depth around the contour of the cutregion. The initial pulses can be of shorter duration, higher amplitudeand shorter period to induce flash vaporization or other cold ablationprocesses, and the pulse sequence transitions to longer pulse durations,lower amplitude, longer period pulses as shown in FIG. 30D.

Additionally examples may be periodic repetition of some designedpulsing pattern to accommodate longer cutting/coagulating cycles or moreabrupt changes in pulse parameters such as combinations of short andlong pulse durations with abrupt transitions to intermix cutting andcoagulating within a multi-pulse exposure. Dynamic pulse variationsallow control and customization of cutting and coagulation effects.

In many embodiments, the laser system has a controllable q-switch 2910capable of generating a pulsed laser output beam. The q-switching can beachieved with acousto-optic, electro-optic, mechanical, saturableabsorbers or other q-switching mechanisms. Most active q-switchingmechanisms can have a power source to enable the q-switching action. Thepower source may be controllable to operate the q-switch 2910 in apulsed mode or an off mode, enabling continuous wave operation. Anymeans to control at least one of the q-switch pulse amplitude, pulseduration or pulse period, preferably all three can be sufficient.Dynamic pulse control may be in the form of one set of pulse parameters,fixed during an exposure, for a given user setting and alternative setsof pulse parameters, fixed during the exposure, for different usersettings. Additionally dynamic pulse control may be in the form of oneor all pulse parameters changing during an exposure in a specified wayfor a given user setting, where each individual user setting may havedifferent parameter changes during an exposure.

FIG. 31A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode for thermaldeposition and coagulation with relatively less tissue cutting.

FIG. 31B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode for efficientcutting of tissue and relatively less thermal deposition.

The user may select between these two pulse series of FIG. 31A or 31B,or many similar variations, depending on the surgical need. Embodimentsallow controlled variations of the q-switch pulse parameters for eachindividual q-switch pulse of a multi-q-switch pulse exposure. Theq-switch pulse parameters may include: amplitude, duration and period.

FIG. 32A shows a non-limiting example of an exemplary output waveform ofthe laser as in FIG. 28B when the system is operated in a q-switchedpulse mode of linearly increasing pulse duration, period and amplitude.A linearly increasing stair case q-switch pulse amplitude with anincreasing q-switch period and increasing q-switch pulse duration.Alternatively this q-switch pulse structure could have a decreasingstair case or pulse period or pulse duration or inter-mixed combinationof increasing, decreasing or static parameters. Also the rate of changefrom pulse to pulse could be non-linear for any one or up to all ofthese parameters.

FIG. 32B shows an example with a decreasing q-switch pulse period anddecreasing pulse duration in a periodic cycle. Alternatively the periodor pulse duration may be increasing or combinations of increases anddecreases. Also the pattern period could be shorter or longer with moreor less substructure pulses. The amplitudes may be varied as well. Thisdynamic q-switch pulse control additionally enables athermal orminimally thermal ablation of hard and soft tissue, including FlashVaporization, and can allow transitions of these athermal or minimallythermal ablations to or from hotter ablations modes.

FIG. 32C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to ablate bone.

For example when a surgeon intends to excise a section of bone thesystem can be adjusted to longer period, higher amplitude q-switchpulses to enable cold ablation, including flash vaporization, of bone,as shown in FIG. 32C.

FIG. 32D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to cut tissue anddeposit more heat to control bleeding. When the surgeon then intends toremove highly vascular soft tissue adjacent to the bone the q-switchpulses can periodically repeat a pattern of long period, high amplitude,short q-switch pulses transitioning into shorter period, lower amplitudeq-switch pulses, to enable efficient cutting while depositing more heatto control bleeding, as shown in FIG. 32D.

FIG. 32E shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to remove a nervesheath. When a surgeon intends to remove a nerve sheath the system couldset to very long q-switch periods with lower amplitude pulses tocarefully ablate the sheath with substantially no thermal deposition inthe nerve itself, the controlled amplitude of the pulses help ensurejust the sheath is ablated, as shown in FIG. 32E.

FIG. 32F shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a q-switched pulse mode to coagulate aruptured vessel. When a surgeon intends to coagulate a ruptured vesselthe system can be set to a short period q-switch pulse sequence,creating a quasi-cw mode, to increase thermal deposit and help coagulatethe vessel, as shown in FIG. 32F.

Additional configurations may comprise periodic repetition of somedesigned q-switch pulsing pattern to accommodate longercutting/coagulating cycles or more abrupt changes in q-switch pulseparameters such as combinations of short and long pulse durations withabrupt transitions to intermix cutting and coagulating within amulti-q-switch pulse exposure. This dynamic q-switch pulse controlallows the tissue interaction to be finely customized to control thecutting rate and amount of thermal damage incurred on the remainingtissue.

FIG. 33 shows the absorption characteristics of blood and water intissue over a broad spectral range, for incorporation in accordance withembodiments of the present invention.

In many embodiments, the gain medium 2900 is relevant to the desiredtissue effects and potentially relevant to the practical pulseparameters of the pump source 2930 and q-switch 2910. General types ofgain mediums may include a solid state crystal, waveguide, polymer, gas,liquid or semi-conductor material. The gain medium 2900 can determinethe allowable output wavelength or wavelength range. The wavelength canbe relevant to surgical laser systems because the wavelength effects howstrongly the light energy can be absorbed by tissue. Gain mediums andtheir respective output wavelengths can be grouped into threecategories: strongly absorbed by water, strongly absorbed by blood andin between, where absorption in both blood and water is relatively weak,as shown in FIG. 33.

Most tissue, including bone, has a higher water content than bloodcontent so wavelengths strongly absorbed by water tend to be morestrongly absorbed in most tissue. One method of enabling a broad dynamicrange of tissue effects is choosing a wavelength that is stronglyabsorbed in tissue, so that in combination with the appropriate pulsingparameters the system can achieve an efficient ‘cold’ cut wherebyleaving, at most, only a shallow coagulation depth in the remainingtissue. Wavelengths strongly absorbed in blood and the ‘in between’wavelengths can also be used to enable a broad dynamic range of tissueeffects, but their ability to create a ‘cold’ cut is more challengingand typically has a more complex and expensive pulsing implementation.Wavelengths that are strongly absorbed in water are preferred. Certaingain mediums can lase efficiently across a broad range of wavelengthsand can thus be tuned to a specific wavelength or wavelength band withinits tunable range. Wavelength tuning can be fixed, user adjustable orvariable during an exposure. Tuning may enhance the systems ability toachieve a desired clinical goal. Thulium types gain mediums like Tm:YAP,Tm:YAG, Tm:YLF, etc are typically strongly absorbed in water and can bereadily transmitted down optical fibers. Tm:YAP has further advantagesfor surgical applications since it lases at 1.94 μm (a peak of waterabsorption) and a broad band of wavelengths above and below the waterabsorption peak. Tm:YAP also has an upper state lifetime of −4 ms andtherefore can be q-switched over a broad range of frequencies with highenergy pulses. Laser systems designed with output wavelengths that arestrongly absorbed by water may implement measures to prevent moisturefrom accumulating on the optical surfaces. Hermetic seal of the lasercavity, desiccants, inert gas purging and other techniques may be usedto keep water from ultimately causing damage to the optical surfaces,including coatings. Similar measures may be used at the waveguidecoupling interface.

In many embodiments the system may incorporate a small core flexiblewaveguide 2980. One advantage of a small and flexible waveguide 2980 isenhanced accessibility. Small waveguides can accommodate small endoscopeworking channels allowing smaller overall diameters of the endoscopeswithout compromising clinical functionality. Flexible waveguidesaccommodate flexible endoscope allowing access to areas where a straightline of access is difficult or impossible and the flexible scopes can doso without increasing the risk to the patient. For example access to themaxillary sinus cavity base through the natural opening of the nostrilrather than a hole cut into the cheek or gums. Additional examplesinclude natural orifice transluminal endoscopic surgery, where forexample a gallbladder is treated via access into the mouth, down theesophagus, a through the stomach wall. An endoscope with limitedflexibility can not be suitable to reach the gallbladder via that path.Additionally a flexible and small diameter endoscope can be more easilymanipulated once the working tip is located at the treatment site,allowing surgeon to have better control to remove just the desiredvolume of tissue. Advances in small flexible scopes have enabled new andclinical beneficial ways to access target areas, although this equipmenthas been primarily for diagnostic purposes, in part, because no suitablesurgical tools exist that can function well with the size, length andflexibility specifications to be compatible for performing treatmentswith these primarily diagnostic tools. An additional advantage of asmall waveguide 2980 is that high irradiances or high fluences can beachieved with lower overall power or energy. For efficient ablation ofhard or soft tissue some threshold energy for a given area should beexceeded. The steady state thermal ablation model is a well acceptedapproximation for both continuous wave and pulsed laser ablation.

Steady-State Ablation Model:V _(ss) =E/p[c(T _(b) −T _(o))+L _(v)]

V_(SS) is the steady state ablation velocity (mm/s)

E is the irradiance (W/mm²)

p is the density (g/mm³)

c is the specific heat (J/g° C.)

L_(v) is the latent heat of vaporization

T_(o) is the initial temperature

T_(b) is the boiling temperature of the irradiate tissue

A pulsed approximation for determining a vaporized volume of water is:V _(ss) =A(Ho−H _(th))/W _(abl)

V_(ss) is the volume of vaporized water (mm³)

A is the incidence area (mm²)

H_(o) is the radiant exposure (J/mm²)

H_(th) is the threshold radiant exposure (J/mm²)

W_(abl) is the total heat of ablation (J/mm³)

Alternative pulsed ablation model is the Blow Off model:V _(bo)=(A/μ _(a))ln(H _(o) /H _(th))

Vb_(o) is the volume of vaporized water (mm³)

A is the incidence area (mm²)

μ_(a) is the absorption coefficient (1/mm)

H_(o) is the radiant exposure (J/mm²)

H_(th) is the threshold radiant exposure (J/mm²)

The energy needed goes down as the ablation area goes down, so smallerfibers with smaller tissue incidence surface areas can use less energyto ablate. As the total energy is reduced the ablated volume can bereduced as well, however when the goals is to excise tissue the ablatedvolume becomes less relevant than the surface area of the ablated volumeto detach the tissue to be removed from the tissue that can remain. Forexample if the goal is to detach a polyp that has a 1 cm² attachmentarea to healthy tissue then it can removed by ablating a 2 mm widesection of the polyp base, resulting in a total ablation volume of 0.2cm³ or it can be removed by ablating a 100 um wide section of the polypbase, resulting in a total ablation volume of 0.001 cm³. Both scenariosremove the polyp, the 100 μm section uses far less total energy to doso. The reduced power or energy that accompany a small treatment spotsize allow the laser system to be scaled down in power and or energyoutput and thus in size and cost. This allows a very small, portable andefficient laser system to perform, at minimum, clinically equivalent totheir larger, more expensive, more powerful counterparts. The reductionof overall system energy or power enables a physically small portablelaser system to be battery operated and may be suitable for field use orwhere standard electrical utilities are not available. With theappropriate choice of wavelength, beam quality and pulse parameters thesmall low power system can outperform existing ablation technologies fortissue removal. Additionally, in-part, due to the small interaction areaand proper parameter choices the collateral damage can be substantiallynon-existent. If some thermal damage is desired, for instance to controlbleeding, then the system parameters can be adjusted such that somethermal damage occurs even with the small interaction area. High beamquality may enable the laser beam to be launched into a small core fiberoptic waveguide 2980. The beam quality is both relative to the abilityto focus down to a small enough spot to enter the waveguide 2980 andalso to have a low enough numerical aperture to operate with minimalloss or damage when the fiber is bent during use.

FIG. 34 shows a laser system with two complimentary output wavelengthsfor implementing a versatile and effective surgical tool with furtherenhanced clinical capabilities, in accordance with embodiments of thepresent invention.

In many embodiments the laser system may have a second wavelength 3010.The second wavelength 3010 can be complimentary in some form, typicallyabsorption characteristics or pulsing characteristics, to the primarywavelength. A second wavelength 3010 may broaden the systems scope ofclinically meaningful tissue interactions, thus helping the surgeonachieve more optimal clinical results for their patients. The secondwavelength 3010 may be independently controlled or intermixed with theprimary wavelength. A routing mirror 3020 and a combining mirror 3030may direct the second wavelength output beam to coincide with theprimary wavelength beam to be coupled into the waveguide 2980. Thesecond wavelength 3010 may include the pump pulsing, q-switch pulsing,gain medium, control system, delivery coupling, delivery system, beamquality and small waveguide features and functionality described herein,including all possible permutations, subsets and continuous waveoperation.

In many embodiments the system may be used interstitially to coagulate,for example cook, ablate or a combination of coagulation and ablation todebulk a tissue mass while leaving the surface tissue substantiallyintact. For example, to reduce the mass of an inferior turbinate, whilegenerally preserving the mucosa, a waveguide can be insertedinterstitially into the submucosal tissue then the laser system canablate by flash vaporization, a mass of tissue, including bone ifdesired, leaving an open cavity inside the sub-mucosal tissue.

FIG. 35 shows a cross-section of an inferior turbinate, showing anexemplary tissue effect of the laser as in FIG. 28B or FIG. 34 lasersystem.

Alternatively or in combination, the system may ablate some mass oftissue and either concurrently, pre-ablation or post ablation coagulatea desired thickness of tissue around the surface of the sub-mucosalcavity, as shown in FIG. 35. Additional embodiments coagulate a mass ofthe sub-mucosal tissue with no substantial tissue ablation. Thesetechniques may each remove tissue mass from the sub-mucosal andpotentially bony regions and facilitate turbinate mass reduction andreduction of the overall size of the turbinate to reduce an airwayobstruction. These interstitial techniques are applicable and effectivefor many other clinical applications as well.

FIG. 36 shows a plot of ablation rate as a function of radiant exposure.In many embodiments the pulse parameters, gain medium and waveguide sizeare selected to optimize the ablation efficiency. The system setting maybe chosen by the user to optimized ablation for different types oftissues. Once above the ablation threshold the ablation rate generallyincreases linearly as the radiant exposure increases. Then as theradiant exposure continues to increase secondary effects can start tooccur that reduce ablation efficiency.

As radiant exposure is further increased the ablation rate can thenbegin to drop due to strong inefficiencies caused by the secondaryeffects, as in FIG. 36. Non-limiting examples of secondary effects mayinclude incident beam scattering from ejected material, mechanicalstress to the surrounding tissue or undesirable ablation crater shapes,for example crater shapes that diminish the efficiency of furtherablation. At the onset of these types of secondary effects the ablationefficiency is still increasing with incident radiant exposure, althoughat a slower rate. Prior art systems are typically optimized for amaximum ablation rates which means they often operate in a regime wheresecondary effects play a role. For Flash Vaporization embodimentsoptimized ablation may be the fastest ablation rate that does not induceundesired secondary effects leading to undesired collateral damage ofthe tissue. Alternatively optimized ablation may be the highest positiverate of change in ablation speed. Clinically this is useful for ablationnear or on sensitive tissue. For example nerve bundles where scatteredlight or mechanical shock waves may be damaging or painful.

Alternative and combinational embodiments include many permutations andsubset permutations of the pump pulsing, q-switch pulsing, gain mediums,small waveguides, second wavelengths and operative techniques describeherein. These permutations provide powerful, effective, versatile andexplicitly customizable performance characteristics to help surgeonremove any tissue with minimal collateral damage, optimal clinicaloutcomes, optimal recovery times, minimal risk and simple operativetechniques. Dynamic pulse permutations may be in a form where the pumpand q-switch pulse parameters are fixed during an exposure for a givenuser setting and alternative sets of pump and/or q-switch pulseparameters are fixed during an exposure for different user settings.Additionally dynamic pulse control may be in the form of one or all pumpand/or q-switch pulse parameters changing during an exposure in aspecified way for a given user setting, where each individual usersetting may have different parameter changes during an exposure. Anon-limiting example may be pulse structures where pump source pulsesequences with dynamic pulse durations, periods and/or amplitudes arecomprised of q-switch pulse sequences with fixed or dynamic q-switchpulse durations, periods and/or amplitudes. A controller or some othermeans to coordinate the pulse timing between the pump source pulses andq-switch pulses may be used. In these embodiments one or more, up to allpump source and q-switch pulse parameters can be varied to operate in afixed or dynamic multi-pulse exposure to optimize the desire clinicaltissue effect.

FIG. 37A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed pump pulse parameters and a shorter q-switch period.

FIG. 37B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed pump pulse parameters and a longer q-switch period.

Some examples include a fixed pump pulse duration, period and amplitudewith a fixed q-switch pulse duration, period and amplitude for one usersetting and a second user setting with the same pump pulse scheme but adifferent q-switch period and amplitude, as in FIGS. 37A & 37B.

FIG. 37C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed q-switch pulse parameters and a longer pump pulse duration.

FIG. 37D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith fixed q-switch pulse parameters and a shorter pump pulse duration.

Another embodiment comprises fixing of the q-switch pulse parameter andpump parameters for one user setting, but vary only the pump pulseduration and amplitude for a different user setting, as in FIGS. 37C &37D.

FIG. 37E shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith a longer pump pulse duration and a longer q-switch pulse period.

FIG. 37F shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith a shorter pump pulse duration and a shorter q-switch pulse period.

Another configuration comprises a fixed pump pulse duration, period andamplitude with a fixed q-switch pulse duration, period and amplitude forone user setting and a second user setting with a different pump pulseperiod, amplitude and a different q-switch period, as in FIGS. 37E &37F.

FIG. 38A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith increasing pump pulse duration and decreasing q-switch pulse periodwithin each pump pulse.

FIG. 38B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modeincreasing pump pulse duration and decreasing q-switch pulse periodacross a multiple pump pulse exposure.

Additional embodiments include a linear step wise increase in pump pulseduration with a substructure of linear step wise decreasing period inthe q-switch pulses, within each pump pulse or across the sequence ofpump pulses, see FIGS. 38A and 38B.

FIG. 38C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an increasing pump pulse duration and a fixed longer q-switch pulseperiod.

FIG. 38D shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an increasing pump pulse duration and a q-switch pulse period thatis fixed during each pump pulse and decreasing with each subsequent pumppulse.

Alternatively with a linear step wise increase in pump pulse duration,each pump pulse may have a fixed q-switch pulse period within thatindividual pump pulse, as in FIG. 38D, and another embodiment comprisesa fixed q-switch period within each individual pump pulse that can bedecreasing with each subsequence pump pulse, as in FIG. 38D. Thesecombinations can be advantageous for a surgeon who wants to begin withless thermal deposition and transition to more thermal deposition.Permutations of these with amplitude variations could also be employedto enhance the clinical effect.

FIG. 39A shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an abrupt transition from less thermal deposition to more thermaldeposition.

Additional examples of starting out with less thermal deposition andtransitioning to more thermal deposition include some initial number ofpump pulses with shorter pulse durations and longer q-switch periods andthen an abrupt transition to longer pulse duration pump pulses withshorter period q-switch pulses, as in FIG. 39A. The q-switch pulsestructure could be dynamically changed during these pump pulses as well.

FIG. 39B shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an abrupt transition from more thermal deposition to less thermaldeposition.

The opposite scenario where the initial pump and q-switch pulsescombinations are such that they deposit more heat initially and theabruptly ablate may be advantageous for harder tissue where the surgeonwould like to deposit substantial heat in the tissue and then use astrongly ablative pulse or pulse sequence to create a fracture, as inFIG. 39B.

FIG. 39C shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith an abrupt transition from more thermal deposition to less thermaldeposition, repeated during each pump pulse.

A hard tissue fracture effect may also be achieved by keeping the pumppulse parameters fixed and abruptly transitioning the q-switch pulseparameters from a low amplitude short period pulse structure to a highamplitude, high energy pulse structure abruptly near the end of eachpump pulse, as in FIG. 39C.

Soft tissue resection with well controlled collateral damage zones mayalso be achieved with dynamic pump and q-switch pulse structures.

FIG. 39D shows the pump source and q-switch modulation individually andthe resulting laser output waveform of the laser as in FIG. 28B when thesystem is operated in a combined q-switched and pump pulse mode with anabrupt transition from more thermal deposition to less thermaldeposition, repeated during each pump pulse. The exemplary combinationof pump pulsing and q-switch pulsing may comprise an abrupt transitionfrom more thermal deposition to less thermal deposition, repeated duringeach pump pulse. The pump and q-switch pulses are shown individuallywith the resulting laser output shown at the bottom.

FIG. 39E shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith the q-switch mode including a continuous wave portion.

Alternative dynamic pulse structures may include continuous waveportions as part of the dynamic pulse structure. By operating theq-switch in the off mode with an appropriate range of pump source power,continuous wave operation can be achieved, as in FIG. 39E.

FIG. 39F shows an exemplary output waveform of the laser as in FIG. 28Bwhen the system is operated in a combined q-switched and pump pulse modewith the q-switch mode including a variable amplitude continuous waveportion.

The pump and q-switch pulses are shown individually with the resultingoutput shown at the bottom. The continuous wave portion of a dynamicpulse scheme may also have variable amplitude, as in FIG. 39F.

FIG. 40 shows an exemplary simple slide bar user interface with dynamicpulsing, in accordance with embodiments of the present invention.

Dynamic pulsing of the pump source and/or the q-switch creates a widearray of pulse structure permutations that can be optimized for specificand finely controlled tissue interactions as well as span substantiallyall interaction types from cold ablation, including flash vaporization,continuously through to pure coagulation without ablation. Furtherembodiments include pulse combinations with small waveguides forimproved cutting efficiencies and better accessibility. Additionally acomplimentary second wavelength can be added to these permutations tobroaden the span of achievable tissue interactions. Also the choice ofgain medium 100 for these embodiments can influence the achievabletissue interactions.

The controller 2940 can be a centralized or distributed system that cancontrol directly or indirectly the parameters of, at least, the pumpsource 2930 or q-switch 2910, preferably both. The controlled parametersmay include pulse duration, pulse amplitude and pulse period. Thecontroller 2940 may be capable of varying combinations of these pulseparameters down to an individual pulse basis. The controller 2940 mayalso operate the system in a non-pulsing mode for example continuouswave or quasi-continuous wave. The controller 2940 may include orcommunicate with directly or indirectly a means to tune the outputwavelength. The controller may have a tangible medium 2950, for exampleknown RAM, ROM and flash memory. The controller 2940 may include orcommunicate with the system's user interface 2960 allowing the user toselect a setting that the controller 2940 may interpret and determineand implement the necessary pulsing scheme to achieve the desired tissueeffect. The controller 2940 may include or communicate with the powersource for the pump source 2930 and/or the q-switch 2910. An exemplaryand relatively simple user interface for dynamic pulsing is shown inFIG. 40. The power adjustment 2961, which can be related to the cuttingrate, may be a knob, slide, button, touch screen or other meaningfulinterface mechanism allows the user to select a power setting. A thermaladjustment 2962 mechanism which may also be a knob, slide, button, touchscreen or other meaningful interface mechanism would control the levelof thermal deposition into the tissue for the given power settingranging from ‘cold’, substantially all ablative with little to noresidual thermal damage, to ‘hot’, substantially all thermal depositionwith little to no ablation.

FIG. 41 shows an exemplary flow diagram for interpreting the usersettings and establishing the laser output pulsing scheme, in accordancewith embodiments of the present invention.

The surgeon may determine the appropriate settings based on the clinicalneed 2963, see the flow diagram FIG. 41. Once the setting are made thecontroller 2940 can prepare the pump pulse configuration 2941, which mayinclude the amplitude, period and pulse duration settings as well as theq-switch pulse configuration 2942, which may include the amplitude,duration and period settings. In this example the internal dynamic pulseparameter settings are within predetermined ranges for specific userinterface input 2964. Those predetermined ranges may be maintained in aportion of the controller tangible medium 2950. In FIG. 41 the userwants to cut soft tissue and maintain moderate bleeding control, such asremoving a polyp attached to highly vascular tissue. The user inputslide bar has been moved to the appropriate location. Now based on theslide position the controller 2940 correlates to a predetermined set ofparameters, see the flow chart of controller 2946, in this case a mediumamplitude, medium duration and short period pulse mode. For anyinter-related parameter dependencies, for example q-switch pulseamplitude and q-switch period, the controller would determine the rangelimits and/or the mix of settings to achieve the desired outcomes asselected by the user. The dynamic predetermined settings may be adjustedduring an internal calibration 2944 cycle to fine tune the parametersand accommodate the user power setting. When calibration is complete thesystem is ready for an exposure 2945. The controller 2940 can coordinatethe timing of the dynamic pulse sequences during an exposure. Manyalternative user interface 2960 and control structures can be used.

FIG. 42 shows an exemplary touch screen user interface for customizingdynamic pulse parameters without transitions during exposures, inaccordance with embodiments of the present invention. In this examplethe dynamic pulse structure can be custom designed by the surgeon. Theuser can press the arrows on the screen to increase or decrease theadjacent parameter. For example the user may be able to select eachpulse parameter: amplitude, duration and period for both the pump pulsesand the q-switch pulses. In this example the ‘TRANSITION RATE’adjustment is set to ‘none’ so the user selected parameters remain fixedduring the exposure.

FIG. 43 shows a flow chart for an exemplary control system for dynamicpulsing with an user interface as depicted in FIG. 42. The controller2940 can limit the range of parameters selections to achievablesettings, allowable parameter combinations 2947, and manage thehierarchy of priority when selections are made. The system can then loadpump and q-switch device controllers with selected parameters 2948. Aninternal calibration 2944 is performed, if necessary some fine tuning ofthe parameters is performed to optimize the system and then the systemis ready for exposure 2945. The controller can coordinate the timing ofthe dynamic pulse sequences during an exposure. FIG. 44 shows anexemplary user interface with a customizable dynamic pulse schemeincluding pulse transitions during the exposure. The user can press thearrows on the screen to increase or decrease the adjacent parameter. Fortransitioning pulse sequences the initial pulse sequence parameters areentered. Additionally the final pulse sequence parameters are entered.The user selects a ‘TRANSITION RATE” varying from slow gradualtransitions to fast abrupt transitions, in the this example thetransition rate is midway between fast and slow.

FIG. 45 shows a flow chart for an exemplary control system withtransitional dynamic pulses with an user interface as depicted in FIG.44. The controller 2940 can limit the range of parameters selections toachievable settings, allowable parameter combinations 2947, and managethe hierarchy of priority when selections are made. For transitionalpulse settings the controller 2940 can compute or use predeterminedvalues to structure the entire pulse sequences including thetransitional pulsing scheme 2949. The system can then load pump andq-switch device controllers with selected parameters 2948. An internalcalibration 2944 is performed, if necessary some fine tuning of theparameters is performed to optimize the system and then the system isready for exposure 2945. The controller can coordinate the timing of thedynamic pulse sequences during an exposure. The controller may interfacewith an user activation switch to active the laser system. The useractivation switch may be a hand or foot activated device and may includemultiple functions.

FIG. 46 shows a laser system using an end-pumping scheme to pump thegain medium, in accordance with embodiments of the present invention.

The resonator cavity may be formed with two mirrors 2920, onepredominately reflecting the lasing wavelength and one partiallytransmissive to the laser output wavelength. The predominatelyreflective mirror may allow the pumping wavelength to pass through themirror enabling the gain medium 2900 to be end pumped with a lasersource 3040, for example diode laser. The intra-cavity elements are atminimum a gain medium 2900 and may include a q-switch 2910. Additionalintra-cavity elements may include: lenses, substances for harmonicgeneration, elements to alter beam quality and various permutations ofthese elements. Cavities with more than two mirrors may also be used. Amirror may also be formed on the surface of an intra-cavity elementrather than a stand alone element.

The coupling optics 2970 direct the laser output beam such that it canbe coupled into a waveguide 2980 and ultimately directed to a treatmentsite. Single, multiple or lens-less configurations can be used as wellas other techniques to direct beams.

The waveguide 2980 is preferably a low OH silica fiber capable oftransmitting IR light up to 2.5 μm. The waveguide 2980 can be made fromother transmissive materials with consideration of the specificwavelength and powers being transmitted. The waveguide 2980 may have asecure recognition device integrated such that the laser system canrecognize when the waveguide is attached. The delivery system mayinclude additional instrumentation to house or hold the waveguide forexample to allow insertion of the waveguide endoscopically. Theinstrumentation may further facilitate manipulation of the waveguide2980 and/or the waveguide tip to perform specific surgical functions.The instrumentation may also include suction, irrigation, visualization,tissue manipulation functionality or their permutations.

In many embodiments beam quality may be an important parameter. Beamquality relates to the clinical tissue effect by effecting beamdivergence at the output of the delivery device tip, thus affecting theirradiance impinged on the tissue. Beam quality also affects the minimalcore size and numerical aperture of a fiber optic deliver device, whichaffects the overall size and practical bend radius of the deliveryfiber. End pumping is a preferred technique to help achieve good beamquality. Other techniques may include apertures, intra-cavitytransmissive elements, thermal management of the gain medium and thegeneral design of the resonant cavity.

Clinically significant wavelengths may span from 170 nm to 15 μm and maybe fixed or tunable.

Clinically significant pump source pulse parameters may span thefollowing ranges:

Peak pulse amplitude from 0.1 W to 10 KW

Energy per pulse from 10 uJ to 24 J

Pulse durations from 0.1 us to 10 s

Pulse periods from 1 us to 10 s

With a resultant average power from 1 mW to 1 KW

Clinically significant Q-switch pulse parameters may span the followingranges:

Peak pulse amplitude from 1 W to 100 MW

Energy per pulse from 10 nJ to 1 J

Pulse durations from 1 ns to 100 us

Pulse periods from 10 ns to single shot

With a resultant average power from 1 mW to 1 KW

Clinically significant combinations of pump pulsing and Q-switch pulsingmay span the permutations for each individually as listed andadditionally span a resultant average power range from 1 mW to 1 KW.

Clinically significant beam quality may range from: M² of 1 to 100

Treatment spot size range from: 10 μm to 10 mm

Clinically significant pump pulse working beam peak power per unit areamay range from:

1 mW/cm² to 125 GW/cm²

Clinically significant Q-switch pulse working beam peak power per unitarea may range from:

1 W/cm² to 500 GW/cm²

Clinically significant working beam average power per unit area mayrange from:

1 W/cm² to 125 GW/cm²

Waveguide core sizes may range from 2 μm to 2 mm, preferably 25 μm to100 μm.

Some non-limiting preferred parameters for a Tm:YAP gain medium:

Clinically significant wavelength may span from 1.8 μm to 2.2 μm and maybe fixed or tunable.

Clinically significant pump source pulse parameters may span thefollowing ranges:

Peak pulse amplitude from 0.5 W to 120 W

Energy per pulse from 0.1 mJ to 24 J

Pulse durations from 10 us to 2 s

Pulse periods from 1 ms to 2 s

With a resultant average power from 1 mW to 12 W

Clinically significant Q-switch pulse parameters may span the followingranges: Peak pulse amplitude from 100 W to 50 MW

Energy per pulse from 1 mJ to 50 mJ

Pulse durations from 5 ns to 500 ns

Pulse periods from single shot to 100 us

With a resultant average power from 0.05 W to 12 W

Clinically significant combinations of pump pulsing and Q-switch pulsingmay span the permutations for each individually as lists andadditionally span a resultant average power range from 0.1 W to 50 W.

Clinically significant beam quality may range from:

M² of 1 to 10

Clinically significant pump pulse working beam peak power per unit areamay range from:

1 KW/cm² to 350 KW/cm²

Clinically significant Q-switch pulse working beam peak power per unitarea may range from:

1 KW/cm² to 750 GW/cm²

Clinically significant working beam average power per unit area mayrange from:

0.5 W/cm² to 100 MW/cm²

Substantially all tissue types are responsive across a broad range oftissue effects when utilizing dynamic pulsing, appropriate gain mediums,small waveguides, or their subsets or permutations, including but notlimited to vascular tissues, avascular tissue, tumors, cysts, nerve,mucosa, submucosa, connective tissues, cartilage, organs and bone. Theinvention disclosed, in part, provides uniquely designed pulsestructures that can sequence or blend the cutting and coagulative tissueeffects in ways advantageous for the surgeon to achieve an optimalclinical result. One clinical benefit of dynamically adjusting the pulseparameters and their permutations is that a surgeon can determine theappropriate level of thermal deposition, across a broad range, tocontrol bleeding during surgery while preserving the viability of theremaining tissue. Another clinical benefit is that dynamic pulse controlenables the removal of both hard and soft tissue. Dynamic pulse controlalso improves visibility for the surgeon during the procedure bycontrolling bleeding, smoke or both. Dynamic pulsing additionally allowsthe trauma to the remaining tissue to be controlled and thus expeditesthe patient recovery time and can also reduce pain and suffering duringthe recovery period. Gain mediums producing wavelengths stronglyabsorbed by water are preferred, but not necessary. These wavelengthsprovide a cost effective means to produce a surgical laser systemencompassing a broad range of tissue effects. A high beam quality lasersystem enabling the use of small core waveguides is also preferred. Thesmall waveguides enable improved accessibility and provides efficienttissue removal with minimal power or energy. Small waveguides are wellsuited for minimally invasive procedures. Providing surgeons with a toolto remove all types of tissue safely and effectively is beneficial forsubstantially all types of surgical procedures. The system is wellsuited for endoscopic natural orifice procedures such as functionalendoscopic sinus surgery, turbinate reductions, head and neck surgeries,colon, rectal, esophageal, bariatric, trans-vaginal, cystoscopic surgeryand others. It is additionally well suited for laparoscopic surgeriessuch as appendectomies, hernia repair, bariatric, cholescystectomy,bowel resection, sterilization and others. Orthopedic, spine,neurologic, brain and traditional open surgeries can benefit as well.Future trends toward natural orifice transluminal endoscopic surgery canalso benefit from a small flexible delivery system with broad andversatility selection of tissue effects.

EXAMPLES

A sinus surgeon performing an ethmoidectomy can remove the centerportion of the thin bony honeycomb like structure and the surroundingmucosa of the ethmoid sinus cavity to improve mucus drainage. Thesurgeon may enter the ethmoid through a mucosa covered bony structurewith minimal bleeding using a periodic pulse scheme such as shown inFIG. 32d . The FIG. 32d pulse scheme periodically blends ablative pulsesfor bone removal with some light heating pulses to control bleeding fromsmall capillaries. Once inside the ethmoid sinus the surgeon mayencounter more bony structures with very thin mucosa where the surgeonmay not be concerned about bleeding issues. In this case the surgeon canswitch setting to a pulse structure such as FIG. 32c where a coldablation, including flash vaporization, of bone is performed with almostno coagulative heating. If at some point during the procedure an arteryis perforated a setting such as FIG. 32f can be used to heat thelocalized area to control bleeding without ablating tissue.

For an inferior turbinate reduction the goal may be to reduce theturbinate's overall size to improve airflow while minimizing damage tothe mucosal tissue layer. A submucosal approach can be used to maximizepreservation of the mucosal layer. A small core fiber delivery device isbeneficial in that it minimizes the size of the trauma area where thedevice is being inserting into the turbinate. During entry and justthrough the mucosal layer a pulsing scheme such as FIG. 39a may be usedto ablate a small hole and deposit a little heat to prevent bleedingfrom small capillaries. Once the fiber is placed in the desired locationsubmucosally, a pulse scheme such as FIG. 37d can be used to efficientlyablate a volume of submucosal tissue. Then a pulse scheme such as FIG.37f can be used to slightly increase the ablation volume and to create amoderate coagulation zone that, in conjunction with the cavity that wasinitially created, can allow the overall turbinate size to be quicklyreduced, improving airflow, preserving a maximal amount of mucosa andfacilitating a rapid patient recovery period.

When removing a gallbladder using a natural orifice transluminalendoscopic technique it can be advantageous to have a very smalldiameter and flexible resection tool to accommodate the long catheterlike instrumentation that is run down the esophagus, into the stomachand through the stomach wall to a location adjacent to the gallbladder.Once properly located it is also advantageous to be able to manipulatethe position of the work tip. A small flexible fiber is well suited forthis type of manipulation. When resecting the gallbladder a pulse schemesuch as FIG. 38d would be advantageous to cut the gallbladder free whilemaintaining a moderate to thick coagulation zone to keep bleeding wellunder control.

For brain surgery a small insertion device 2990 may be advantageous toreach the volume to be removed with minimal impact to tissue in theaccess path. Resection can be performed with thin uniform coagulationcontrol such as the pulse scheme shown in FIG. 30d to control bleeding.Then the partially separate mass to be removed can be ablated using apulse scheme such as FIG. 32c . The ablated tissue remains could beremoved via a small suction path.

FIG. 47 shows general representations of tissue effects caused byexemplary dynamic pulse configurations. The pulsed treatment beam asreferenced in FIG. 32c shows the ablative removal of tissue with noappreciable thermal damage to the remaining tissue. The pulsed treatmentbeam as referenced in FIG. 37b shows primarily ablative removal oftissue with a small amount of thermal damage to the remaining tissue.The pulsed treatment beam as referenced in FIG. 37c shows ablativeremoval of tissue with a moderate amount of thermal damage to theremaining tissue. The pulsed treatment beam as referenced in FIG. 37ashows ablative removal of a small amount of tissue with a large amountof thermal damage to the remaining tissue. Finally the pulsed treatmentbeam as referenced in FIG. 32f shows a large area of coagulated tissuewith no appreciable ablative removal of tissue.

FIG. 48 shows the timing sequence of tissue effects for therepresentative dynamic pulse scheme as shown in FIG. 32d . Time 1represents the first 4 high amplitude, long period, short durationpulses effective at ablating tissue with no appreciable thermal damageto the remaining tissue. Time 2 represents the transitional pulses withconsecutive reductions in amplitude and period and a lengthening ofpulse duration. The transitional pulses continue to ablate, but withless efficiency and begin to deposit some heat in the remaining tissue.Time 3 represents the lower amplitude, shorter period, longer durationpulse series that primarily deposit heat in the tissue withoutappreciable ablation. Time 4 shows the ablative pulse series beingrepeated creating a deeper ablation zone. Time 5 shows the transitionalpulse series being repeated modestly increasing the ablation zone depthand creating an additional thin coagulation zone. Time 6 shows theprimarily thermal pulse series being repeated adding thermal damage tothe remaining tissue. The periodic sequence may continue repeatingthroughout the duration of the exposure.

The diverse range of tissue interactions and surgical capabilitiescoupled with the portability and a self contained power source, such asa battery, make the system advantageous for field use. Surgicalinterventions can be performed in emergency, rescue and military fieldsituations. Additionally the advantages of a Flash Vaporization systemare well suited for robotic surgery.

It should be appreciated that the processor described above may comprisea processor system having one or more processors, and that the tangiblemedium of the processor may comprise a computer program configured toimplement the methods of tissue treatment illustrated above, for examplein accordance with the pulse sequences described above.

It should be appreciated that the specific steps illustrated in the flowdiagrams above provide a particular methods of treating a patient,according to embodiments of the present invention. Other sequences ofsteps may also be performed according to alternative embodiments. Forexample, alternative embodiments of the present invention may performthe steps outlined above in a different order. Moreover, the individualsteps illustrated in the figures may include multiple sub-steps that maybe performed in various sequences as appropriate to the individual step.Furthermore, additional steps may be added or removed depending on theparticular applications. One of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

While the exemplary embodiments have been described in some detail, byway of example and for clarity of understanding, those of skill in theart will recognize that a variety of modifications, adaptations, andchanges may be employed. Hence, the scope of the present inventionshould be limited solely by the appended claims.

We claim:
 1. A system for treating tissue, the system comprising: alaser to generate a laser beam; a controller which controls the laser inresponse to parameters including pulse length and pulse energy; and auser interface connected to controller, said interface comprising a userselectable adjustment to select first and second modes; wherein thecontroller adjusts the laser to operate successively in the first modewith a first set of adjustable parameters and the second mode with asecond set of adjustable parameters, and wherein the controller causesdynamic transition between the first and second modes during anexposure; and a beam delivery device coupled to the laser to deliver thelaser beam to target tissue during the exposure; wherein the controllercontrols both a q-switch and a pump source, and the first set ofparameters includes a first set of q-switch parameters and a first setof pump pulse parameters which cause generation of one or more pulseseach having both a pulse width between 1 ns and 500 ns and a fluence atthe treatment site between 5 J/cm2 and 500 J/cm2 and the second set ofparameters includes a second set of q-switch parameters and a second setof pump pulse parameters, wherein the q-switch is in the off mode, whichcause generation of an average irradiance at a treatment site between500 W/cm2 and 1 MW/cm2.
 2. The system of claim 1, wherein a pulse periodbetween each pulse of said first mode is between 200 us and 200 ms. 3.The system of claim 1, wherein the laser beam has a treatment spot sizebetween 10 μm and 300 μm.
 4. The system of claim 1, wherein the laserbeam has a wavelength between 1.8 μm and 2.2 μm.
 5. The system of claim1, wherein the laser beam has a wavelength in a range of 1.92 to 2.01μm.
 6. The system of claim 1, wherein the laser has a gain mediumcomprising Tm doped host.
 7. The system of claim 1, wherein the laserhas a gain medium comprising Ho doped host.
 8. The system of claim 1,wherein the laser gain medium is end pumped.
 9. The system of claim 1,wherein the laser beam has an M2, which is less than
 10. 10. The systemof claim 1, wherein the system further comprises a silica core waveguideto deliver the laser energy to the treatment site.
 11. The system ofclaim 10, wherein the waveguide core diameter is between 25 μm and 150μm.
 12. The system of claim 1, wherein the user selectable adjustment ispresented on the user interface in terms of an adjustable depth ofthermal damage.
 13. The system of claim 12 wherein the adjustable depthof thermal damage represented on the user interface ranges between 0 μmand 2 mm.
 14. The system of claim 1, wherein in one of the first andsecond modes the laser beam causes a depth of thermal damage in thetarget tissue during the exposure of less than 50 μm.
 15. The system ofclaim 1, wherein, the dynamic pulse sequence comprises periodicrepetition of a pulsing pattern that intermixes cutting pulses accordingto a first set of pulse parameters and coagulating pulses according to asecond set of pulse parameters.
 16. The system of claim 15, wherein thelaser beam has a wavelength between 1.8 μm and 2.2 μm.
 17. The system ofclaim 15, wherein the laser has a gain medium comprising Tm doped host.18. A system for treating tissue, the system comprising: a laser togenerate a laser beam; a controller which controls the laser in responseto parameters including pulse length and pulse energy; and a userinterface connected to controller, said interface comprising a userselectable adjustment to select first and second modes; wherein thecontroller adjusts the laser to operate successively in the first modewith a first set of adjustable parameters and the second mode with asecond set of adjustable parameters, and wherein the controller causesdynamic transition between the first and second modes during anexposure; and a beam delivery device coupled to the laser to deliver thelaser beam to target tissue during the exposure; wherein the controllercontrols both a q-switch and a pump source, and the first set ofparameters includes a first set of q-switch parameters and a first setof pump pulse parameters generating one or more pulses each having botha pulse width between 1 ns and 500 ns and a fluence at a treatment sitebetween 5 J/cm2 and 500 J/cm2, and the second set of parameters includesa second set of q-switch parameters and a second set of pump pulseparameters with one or more pulses each having both a pulse width of atleast 1.2× greater than the pulse width of the first mode and a fluenceat a treatment site of at least 0.8× less than the fluence at thetreatment site of the first mode.
 19. The system of claim 18, wherein,the dynamic pulse sequence comprises periodic repetition of a pulsingpattern that intermixes cutting pulses according to a first set of pulseparameters and coagulating pulses according to a second set of pulseparameters.
 20. The system of claim 18, wherein the laser beam has awavelength between 1.8 μm and 2.2 μm.
 21. The system of claim 18,wherein the laser has a gain medium comprising Tm doped host.